Pneumatic tire having directional tread pattern

ABSTRACT

The present invention provides a pneumatic tire which can obtain a high wet drainage performance, roadholding ability, and wear-resistant property without sacrificing other capabilities A directional pattern is formed by a circumferential wide major groove, a first narrow circumferential minor groove, a second narrow circumferential minor groove, a first transverse groove, a second transverse groove, and a third transverse groove. The circumferential wide major groove is provided in a center region in a tire width direction of a tread. The first narrow circumferential minor groove is arranged on the outside in a tire axis direction of the circumferential wide major groove. The second narrow circumferential minor groove is arranged on the outside in the tire axis direction of the first narrow circumferential minor groove. The first transverse groove is extended from a tread end and coupled to the circumferential wide major groove. The second transverse groove is arranged between the first transverse grooves, and the second transverse groove is extended from the tread end and terminated while not coupled to the circumferential wide major groove. The third transverse groove is arranged between the first transverse groove and the second transverse groove, and the third transverse groove is extended from the tread end and terminated between the first narrow circumferential minor groove and the second narrow circumferential minor groove.

TECHNICAL FIELD

The present invention relates to a pneumatic tire, particularly to thepneumatic tire which can obtain a high wet drainage property withoutsacrificing other capabilities.

BACKGROUND ART

In the pneumatic tire, a circumferential groove and a transverse grooveare arranged in a tread to obtain wet performance (see Patent Documents1 to 3).

Conventionally, in the pneumatic tire, various devices are made toimprove tire performance (for example, see Patent Documents 4 to 7). Inorder to improve the drainage on a wet road surface, a groove volume isincreased by increasing a groove width or a groove depth.

In a racing ultra-high performance vehicle tire, a technique of linearlyarranging several circumferential grooves in a center region of thetread is taken to improve hydroplaning performance, and the techniqueincreases a negative ratio.

Patent Document 1: Japanese Patent Laid-Open No. 57-194106 (FIG. 2)

Patent Document 2: Japanese Patent Laid-Open No. 3-10911 (FIGS. 1 and 2)

Patent Document 3: Japanese Patent Laid-Open No. 11-189011 (FIG. 1)

Patent Document 4: Japanese Patent Laid-Open No. 2001-225611

Patent Document 5: Japanese Patent Laid-Open No. 10-100615

Patent Document 6: Japanese Patent Laid-Open No. 2003-320814

Patent Document 7: Japanese Patent Laid-Open No. 63-061606

DISCLOSURE OF THE INVENTION Subjects to be Addressed by the Invention

However, when the groove width or the groove depth is increased, aground contact area is decreased on the dry road surface, and a shortageof rigidity may be cased in a land portion, which may result in lowerroadholding ability on the dry road surface. An uneven wear-resistantproperty may be also decreased.

The following countermeasures are effective in improving the roadholdingability or the pattern noise property on the dry road surface. That is,the grove area is decreased to increase the ground contact area, and astep-shape bottom raising portion is provided in the transverse grooveof an end portion of the land portion to enhance block rigidity.

However, in the above countermeasures, the groove volume is decreasedand turbulence is generated in a water flow to affect the drainageproperty by the step, which results in drainage property and theroadholding ability to be decreased on the wet road surface.

In the racing ultra-high performance vehicle tire, a hydroplaningphenomenon is easily generated because of high running speed. In aracing ultra-high performance vehicle rear-tire, the hydroplaningphenomenon is easily generated from a low speed region because of wideground contact width. Therefore, such techniques are taken as wideningthe groove width to increase the negative ratio or arranging the severallinear major grooves in the center region so as to solve thehydroplaning phenomenon. However, the area of the land portion isdecreased in the center region and a block width is also decreased,which results in a decrease in grip and a decrease in wear-resistantproperty.

In the racing ultra-high performance vehicle tire, a technique ofcontinuously arranging rib-shape land portions in a central region in atire axis direction is taken to improve handling performance. The landportions are continuously formed in the tire circumferential direction.However, the drainage property of the central region in the tire axisdirection toward the tire width direction is decreased to cause the wetdrainage property to be decreased in the central region in the tire axisdirection.

In view of the foregoing, an object of the invention is to provide apneumatic tire which can obtain a high wet drainage performance withoutsacrificing other capabilities (such as roadholding ability, patternnoise property, and wear-resistant property).

Means for Addressing the Subject

One aspect of the exemplary embodiments provides a pneumatic tire whichhas at least one circumferential wide major groove, plural transversegrooves, and a narrow circumferential minor groove. The circumferentialwide major groove is provided in a center region in a tire widthdirection of a tread, the circumferential wide major groove is extendedin a tire circumferential direction. The transverse groove is providedin the tread and extended from a tread end toward the circumferentialwide major groove while inclined with respect to the tirecircumferential direction. The narrow circumferential minor groove isarranged on an outside in a tire axis direction of the circumferentialwide major groove and is extended in the tire circumferential direction.A groove width of the narrow circumferential minor groove is setnarrower than that of the circumferential wide major groove. The treadhas plural blocks which are zoned by the circumferential wide majorgroove, the transverse groove, and the narrow circumferential minorgroove, the tread has a directional tread pattern in which eachtransverse groove being sequentially in contact with a road surface froma tire equatorial plane side toward the tread end during an on-loadrotating operation. A width and a depth of the narrow circumferentialminor groove in an area where the narrow circumferential minor groovezones the block are decreased from a kick-out side toward a stepping-onside of with respect to the block during the on-load rotating operation.

According to an aspect of the exemplary embodiments, the pneumatic tirehas a directional pattern. Therefore, in the wet road surface driving,the water flows efficiently into the circumferential wide major groove,narrow circumferential minor groove, and transverse groove to obtain thehigh wet performance.

Because the high wet performance is obtained while the increase innegative ratio is suppressed, a wheel tread area of the block is securedto improve the wear-resistant property.

The handling performance is improved because the block rigidity isincreased in the central region in the tire axis direction

Furthermore, during the on-load rotating operation, the width and depthof the narrow circumferential minor groove are decreased from thekickout side toward the stepping-on side of the block in the range wherethe block is zoned by the narrow circumferential minor groove.Therefore, the block rigidity is increased at the stepping-on side ofthe block that is positioned on both sides of the narrow circumferentialminor groove. This improves the traction performance, brake performance,and cornering performance.

As used herein, the term “central region in tire width direction oftread” shall mean a central region when the tread is equally dividedinto three regions in the tire axis direction.

Another aspect of the exemplary embodiments of the pneumatic tireprovides that the at least two narrow circumferential minor grooves areprovided on the outside in the tire axis direction of thecircumferential wide major groove, and the transverse groove includes afirst transverse groove, a second transverse groove, and a thirdtransverse groove. The first transverse groove is extended from thetread end and is coupled to the circumferential wide major groove whileintersecting with the narrow circumferential minor grooves. The secondtransverse groove is arranged between the first transverse grooves, thesecond transverse groove is extended from the tread end and intersectswith the narrow circumferential minor grooves, the second transversegroove is terminated while not coupled to the circumferential wide majorgroove. The third transverse groove is arranged between the firsttransverse groove and the second transverse groove, is extended from thetread end and terminated between the two narrow circumferential minorgrooves.

According to an aspect of the exemplary embodiments, the firsttransverse groove, the second transverse groove, and the thirdtransverse groove are arranged in the tread. The first transverse grooveis extended from the tread end, and the first transverse groove iscoupled to the circumferential wide major groove while intersecting withthe narrow circumferential minor groove. The second transverse groove isarranged between the first transverse grooves, the second transversegroove is extended from the tread end while intersecting with the narrowcircumferential minor groove, and the second transverse groove isterminated while not coupled to the circumferential wide major groove.The third transverse groove is arranged between the first transversegroove and the second transverse groove, and the third transverse grooveis extended from the tread end and terminated between the two narrowcircumferential minor grooves. Therefore, the length in the tirecircumferential direction of the block zoned by the grooves can besequentially formed to become a half from the tire equatorial plane sidetoward the tread end, and the wet drainage property can be increased onboth sides of the tread while the block rigidity can be increased on thetread central region side to increase the traction performance, brakeperformance, and cornering performance.

Another aspect of the exemplary embodiments provides that tireequatorial plane-side terminal positions of the second transverse grooveand third transverse groove are located in a central region of a blockin the tire axis direction.

The tire equatorial plane-side terminal positions of the secondtransverse groove and third transverse groove are located in the centralregion in the tire axis direction of the block where each of the secondtransverse groove and third transverse groove is arranged. Therefore,the high wet drainage property, roadholding ability, and wear-resistantproperty can be obtained in a preferable manner.

When the tire equatorial plane-side terminal positions of the secondtransverse groove and third transverse groove are shifted to the outsidein the tire axis direction from the central region in the tire axisdirection of the block, the water existing on the block surface hardlyflows into each transverse groove, and thereby the wet drainage propertyis undesirably decreased.

When the tire equatorial plane-side terminal positions of the secondtransverse groove and third transverse groove are shifted to the inside(tire equatorial plane side) in the tire axis direction from the centralregion in the tire axis direction of the block, undesirably the blockrigidity is lowered to decrease the traction performance, brakeperformance, and cornering performance.

As used herein, the term “central region of block in tire axisdirection” shall mean a central region when the block is equally dividedinto three regions in the tire axis direction.

Another aspect of the pneumatic tire provides that, assuming that W2 isa groove width of the first transverse groove, W3 is a groove width ofthe second transverse groove, and W4 is a groove width of the thirdtransverse groove, W3 is set in a range of 60% to 110% of W2 and W4 isset in a range of 20% to 60% of W2.

Assuming that W2 is a groove width of the first transverse groove, W3 isa groove width of the second transverse groove, and W4 is a groove widthof the third transverse groove, W3 is set in a range of 60% to 110% ofW2 and W4 is set in a range of 20% to 60% of W2. Therefore, a balancecan be achieved between the wet drainage property and the block rigidityin the region surrounded by the first transverse groove and the secondtransverse groove.

The groove width W3 of the second transverse groove is set in a range of60% to 110% of groove width W2 of the first transverse groove, whichallows the groove width W3 of the second transverse groove to beapproximately equalized to the groove width W2 of the first transversegroove to secure the high wet drainage property.

When the groove width W4 of the third transverse groove becomes lowerthan 20% of the groove width W2 of the first transverse groove,undesirably the wet drainage property is decreased in the regionsurrounded by the first transverse groove and the second transversegroove.

On the other hand, when the groove width W4 of the third transversegroove becomes more than 60% of the groove width W2 of the firsttransverse groove, undesirably the block rigidity is decreased in theregion surrounded by the first transverse groove and the secondtransverse groove.

Another aspect of the exemplary embodiments provides that the at leasttwo narrow circumferential minor grooves are provided on the outside ofthe circumferential wide major groove in the tire axis direction, thetransverse groove includes a first transverse groove and a secondtransverse groove, the first transverse groove being extended from thetread end, the first transverse groove being coupled to thecircumferential wide major groove while intersecting with the narrowcircumferential minor grooves, the second transverse groove beingarranged between the first transverse grooves, the second transversegroove being extended from the tread end, the second transverse grooveintersecting with the narrow circumferential minor groove on anoutermost side in the tire axis direction while not intersecting withthe narrow circumferential minor groove on an innermost side in the tireaxis direction, the second transverse groove being terminated while notcoupled to the circumferential wide major groove. The first transversegroove has a bottom raising portion on a side that locates at thecircumferential wide major groove side and a groove depth is graduallydecreased from a start point provided at the outside with respect to thecircumferential wide major groove toward the circumferential wide majorgroove in the tire axis direction at the bottom raising portion.

According to an aspect of the exemplary embodiments, in the wet roadsurface driving, the water near the central region in the tire axisdirection flows into the circumferential wide major groove, and otherwater flows into the first transverse groove. The water on the wheeltread of the block surrounded by the circumferential wide major grooveand first transverse groove flows into the two grooves of the narrowcircumferential minor groove and the second transverse groove. The treadhas the directional patter. Therefore, in the wet road surface driving,the water flows efficiently into the circumferential wide major groove,narrow circumferential minor groove, first transverse groove, and secondtransverse groove to obtain the high wet performance.

Because the high wet performance is obtained while the increase innegative ratio is suppressed, the wheel tread area of the block issecured to improve the wear-resistant property.

According to an aspect of the exemplary embodiments, the firsttransverse groove has the bottom raising portion at the circumferentialwide major groove side thereof, and the groove depth is graduallydecreased from the start point on the outside in the tire axis directiontoward the circumferential wide major groove. Therefore, in the wet roadsurface driving, the water near the central region in the tire axisdirection is distributed by the bottom raising portion into the waterflowing, that is one flowing is toward into the circumferential widemajor groove and the other flowing is toward into the first transversegroove, thereby the wet drainage property is further improved.

The bottom raising portion can suppress the generation of waterturbulence in the circumferential wide major groove to improve the wetdrainage property.

The bottom raising portion reinforces the blocks on both sides of thebottom raising portion, so that the block rigidity is increased in thetread central region to improve the traction performance, brakeperformance, and cornering performance.

As used herein, the term “first transverse groove is coupled tocircumferential wide major groove” shall mean that the first transversegroove is opened to the circumferential wide major groove while thegroove depth of the first transverse groove is not more than 10% ofitself (not including groove depth of 0 mm), or, when the groove depthof the first transverse groove is 0 mm in the opening portion on thecircumferential wide major groove side, the width of the firsttransverse groove is not more than 3 mm in the tire axis direction atthe opening region where the groove depth is 0 mm.

Another aspect of the exemplary embodiments provides that a length ofthe bottom raising portion in the tire axis direction is set in therange of 60 to 200% of a groove width of the circumferential wide majorgroove.

The size of the bottom raising portion in the tire axis direction is setin the range of 60 to 200% of the groove width of the circumferentialwide major groove. Therefore, the wet drainage property can securely beimproved by achieving an excellent balance between an amount of waterflowing into the circumferential wide major groove and an amount ofwater flowing into the first transverse groove.

Another aspect of the exemplary embodiments provides that a depth of atop portion of the bottom raising portion is set to 10% or less of agroove depth of the first transverse groove when each depth is measuredfrom a wheel tread surface of the tread.

When the depth of the top portion of the bottom raising portion is morethan 10% of the groove depth of the first transverse groove in measuringthe depth from the wheel tread surface (namely, when the groove depth inthe bottom raising portion of the first transverse groove is more than10% of the groove depth of the portions except for the bottom raisingportion), the turbulence is generated in the water flowing in thecircumferential wide major groove to decrease the wet drainage property,and the block rigidity is decreased in the tread central region (becausethe block reinforcement effect by the bottom raising portion isdecreased). Therefore the traction performance, brake performance, andcornering performance cannot be improved.

Another aspect of the exemplary embodiments provides that the groovewidth of the second transverse groove is set in the range of 10 to 80%of the groove width of the first transverse groove.

The groove width of the second transverse groove is set in the range of10 to 80% of the groove width of the first transverse groove, whichallows a balance to be achieved between the wet drainage property andthe block rigidity of the outside region in the tire axis direction ofthe tread.

When the groove width of the second transverse groove is lower than 10%of the groove width of the first transverse groove, a shortage of thegroove volume is generated in the second transverse groove to decreasethe wet drainage property.

On the other hand, when the groove width of the second transverse grooveexceeds 80% of the groove width of the first transverse groove, becausethe wheel tread area is decreased in the outside region in the tire axisdirection of the tread, the block rigidity is decreased to affect thecornering performance.

Another aspect of the exemplary embodiments provides that the narrowcircumferential minor groove arranged on the outermost side in the tireaxis direction is inclined toward a direction in which the narrowcircumferential minor groove is sequentially in contact with the roadsurface from the tire equatorial plane side toward the tread end of thenarrow circumferential minor groove during the on-load rotatingoperation.

In the plural narrow circumferential minor grooves, the narrowcircumferential minor groove arranged on the outside in the tire axisdirection is inclined toward the direction in which the narrowcircumferential minor groove is sequentially in contact with the roadsurface from the tire equatorial plane side toward the tread end duringthe on-load rotating operation. Therefore, the wet drainage performanceis improved near both the outsides in the tire axis direction in thetire ground contact portion.

Another aspect of the exemplary embodiments provides that, in the narrowcircumferential minor groove, a groove wall on the tire equatorial planeside is linearly extended in the tire circumferential direction and hasan angle with respect to a normal set to the wheel tread ranges from 40degrees to 80 degrees.

The groove wall on the tire equatorial plane side of the narrowcircumferential minor groove is linearly extended in the tirecircumferential direction, and the angle with respect to the normal setto the wheel tread is set in the range of 40 degrees to 80 degrees(measured on the included angle side). Therefore, a balance can beachieved between the block rigidity of the block at the tire equatorialplane side of the narrow circumferential minor groove and the wetdrainage property of the narrow circumferential minor groove.

When the angle with respect to the normal set to the wheel tread becomeslower than 40 degrees in the groove wall at the tire equatorial planeside of the narrow circumferential minor groove, undesirably the blockrigidity is decreased on the tire equatorial plane side of the narrowcircumferential minor groove.

On the other hand, when the angle with respect to the normal set to thewheel tread becomes exceeds 80 degrees in the groove wall at the tireequatorial plane side of the narrow circumferential minor groove,undesirably a shortage of the groove volume is generated in the narrowcircumferential minor groove to decrease the wet drainage property.

Another aspect of the exemplary embodiments provides that, in the narrowcircumferential minor groove, the groove wall at the tire equatorialplane side is coupled to the opposing groove wall at the outside in thetire axis direction at the stepping-on side with respect to the block.

In the narrow circumferential minor groove, on the kickout side of theblock, the groove wall at the tire equatorial plane side is not coupledto the opposing groove wall at the outside in the tire axis direction.However, on the stepping-on side of the block, the groove was on thetire equatorial plane side is coupled to the opposing groove wall on theoutside in the tire axis direction.

The groove wall on the tire equatorial plane side is coupled to theopposing groove wall on the outside in the tire axis direction.Therefore, the block rigidity can be enhanced on the outside of thenarrow circumferential minor groove in the tire axis direction toimprove the traction performance, brake performance, and corneringperformance.

Another aspect of a pneumatic tire has plural grooves including atransverse groove in a tread, the transverse groove being extended whileinclined with respect to a tire circumferential direction, and a bottomraising portion which raises the bottom of the transverse groove isformed on one side of the transverse groove in a tire width direction,and thereby the transverse groove is substantially opened to andterminated in another groove which is adjacent to the transverse grooveon the one side in the tire width direction, the transverse groove iscompletely opened to other groove which is adjacent to the transversegroove on the other side in the tire width direction or the transversegroove is completely opened to a tread end, and the bottom raisingportion forms an inclined surface at the grove bottom surface, a depthof the transverse groove to the inclined surface being graduallydecreased from the other side to a top portion of the bottom raisingportion in the tire width direction.

As used herein, the term “transverse groove is substantially opened toand terminated in another groove” shall mean that the terminal of thetransverse groove is opened to another groove while the depth of thetransverse groove is not more than 20% of the maximum depth thereof, ora portion whose groove depth is 0 mm is formed in the terminal and thelength (width) in the tire width direction is not more than 3 mm in theportion where the groove depth is 0 mm.

The term “transverse groove is completely opened to other groove” shallmean that the transverse groove is opened while the opening depth of thetransverse groove is larger than 20% of the maximum depth.

According to an aspect of the exemplary embodiments, the directionaltread wheel pattern is formed in the wheel tread portion and the bottomraising portion is formed in the transverse groove. Therefore, in thewet road surface driving, the water near the bottom raising portion isdistributed into the water flow, one flows into another groove on oneside in the tire width direction (one side in tire axis direction) ofthe transverse groove and the other flows toward the other side in tirewidth direction through the transverse groove caused by the inclinedsurface. Therefore, the pneumatic tire having the excellent wet drainageproperty can be obtained.

The roadholding ability on the dry road surface, uneven wear-resistantproperty, and pattern noise property are improved because the rigidityis enhanced in the corner portion of the adjacent land portion by thebottom raising portion provision. This effect is remarkably exhibited inthe corner portion which has an acute angle when viewed from the tiresurface side, i.e., from the wheel tread side.

When one side in tire width direction of the transverse groove is openedto another groove at the position where the depth of the transversegroove is deeper than 20% of the maximum depth thereof, undesirably theblock rigidity is decreased in the tread central region to decrease thetraction performance, brake performance, and cornering performance whilethe turbulence is generated in the water flowing in another groove todecrease the wet drainage property. When the portion whose groove depthis 0 mm is formed in the one side in tire width direction of thetransverse groove and, at the same time, the length (width) in the tirewidth direction is not more than 3 mm in the portion where the groovedepth is 0 mm, undesirably a shortage of the groove volume is generatedin the transverse groove to decrease the drainage property in the wetroad surface. The unfavorable property is not generated because the oneside in tire width direction of the transverse groove is substantiallyopened to and terminated in another groove. The plural grooves includeat least the transverse groove, and the plural grooves may include thegroove except for the transverse groove, e.g., the circumferential majorgroove. Another groove may be extended along the tire circumferentialdirection or another groove may be inclined with respect to the tirecircumferential direction.

Another aspect of the exemplary embodiments provides that the transversegrooves may be formed at substantially equal intervals.

Another aspect of the exemplary embodiments provides that a length of agroove portion which has the inclined surface as a groove bottom surfaceis set in the range of 5 to 100% of a groove length of the transversegroove having the groove portion.

When the groove portion is shorter than 5% of the groove length of thetransverse groove having the groove portion, the rigidity is decreasedin the corner portion of the land portion adjacent to the bottom raisingportion, and sometimes undesirably the roadholding ability on the dryroad surface, uneven wear-resistant property, and pattern noise propertyare largely decreased. In the corner portions, this is remarkablyexhibited in the corner portion which has an acute angle when viewedfrom the wheel tread side. When the groove portion is longer than 100%of the groove length of the transverse groove having the groove portion,the inclined surface is projected to another groove (such as thecircumferential major groove) to obstruct the water flow in anothergroove, and undesirably the wet drainage property is decreased.

According to an aspect of the exemplary embodiments, the undesirableproperty is not generated because the groove length of the grooveportion ranges from 5 to 100% of the groove length of the transversegroove.

Another aspect of the exemplary embodiments provides that the treadincludes a circumferential major groove which is extended along the tirecircumferential direction, a cross section of the bottom raising portionin a longitudinal direction of the groove is formed in a chevron shape,a one side inclined surface is formed as the grove bottom surface at thebottom raising portion, the groove depth is gradually increased from thetop portion to the one side at the one-end-side inclined surface in tirewidth direction, a land portion adjacent to the transverse groove has anedge portion at the one side, the edge portion has an edge surface whichis provided along the circumferential major groove and is chamfered in atapered shape so that the edge surface forms the same surface as the oneside inclined surface, and inclination angles of the one side inclinedsurface and the edge surface range from 30 to 60° with respect to a lineparallel to a tire radial direction.

According to an aspect of the exemplary embodiments, the one sideinclined surface has the same surface as the edge surface. Therefore,the rigidity is enhanced in the edge portion to improve the roadholdingability or uneven wear-resistant property in the dry road surface andwet road surface. In the wet road surface driving, the wet drainageproperty is further improved because the water on the land portionsurface near the edge portion flows into circumferential major groovewithout generating the turbulence.

The one side inclined surface has the same surface as the edge surface,and the groove bottom terminal formed by the bottom raising portioncoincides with the edge end of the edge surface at the circumferentialmajor groove. Therefore, the water flows in the circumferential majorgroove while distributed without generating the turbulence. This alsocontributes to the improvement of the wet drainage property.

When the inclination angle is lower than 30°, in the wet road surfacedriving, undesirably the turbulence is generated when the water on theland portion surface near the edge portion flows into thecircumferential major groove, and the wet drainage property is easilydecreased. When the inclination angle is larger than 60°, because ashortage of the groove volume is easily generated in the circumferentialmajor groove adjacent to the edge portion, undesirably the wet drainageproperty is easily decreased in the wet road surface driving. Accordingto an aspect of the exemplary embodiments, the above trouble is nevergenerated because the inclination angle is set in the range of 30 to60°.

Effect of the Invention

Because the pneumatic tire of the invention has the aboveconfigurations, the pneumatic tire has the excellent effect that thehigh wet drainage performance can be obtained without sacrificing othercapabilities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a tread of a pneumatic tire according to afirst embodiment of the invention;

FIG. 2A is an enlarged plan view of the tread;

FIG. 2B is a sectional view taken on line 2B-2F of a first narrowcircumferential minor groove;

FIG. 2C is a sectional view taken on line 2C-2C of the first narrowcircumferential minor groove;

FIG. 2D is a sectional view taken on line 2D-2D of a second narrowcircumferential minor groove;

FIG. 2E is a sectional view taken on line 2E-2E of the second narrowcircumferential minor groove;

FIG. 3 is a plan view showing a tread of a pneumatic tire according to asecond embodiment of the invention;

FIG. 4A is an enlarged plan view of the tread;

FIG. 4B is a sectional view taken on line 4B-4B of a first narrowcircumferential minor groove;

FIG. 4C is a sectional view taken on line 4C-4C of the first narrowcircumferential minor groove;

FIG. 4D is a sectional view taken on line 4D-4D of a second narrowcircumferential minor groove;

FIG. 4E is a sectional view taken on line 4E-4E of the second narrowcircumferential minor groove;

FIG. 5A is a sectional view taken on line 5-5 of a bottom raisingportion shown in FIG. 3;

FIG. 5B is a sectional view showing a bottom raising portion accordingto another embodiment;

FIG. 5C is a sectional view showing a bottom raising portion accordingto still another embodiment;

FIG. 6 is a plan view showing a tread of a pneumatic tire according toanother embodiment;

FIG. 7 is a sectional view in a tire axis direction of a pneumatic tireaccording to a third embodiment;

FIG. 8A is a plan view showing a tread of a pneumatic tire according tothe third embodiment;

FIG. 8B is a sectional view taken on line 8B-8B of FIG. 8A;

FIG. 9A is a plan view showing a tread of a pneumatic tire according toa fourth embodiment;

FIG. 9B is a sectional view taken on line 9B-9B of FIG. 9A;

FIG. 10A is a plan view showing a tread of a pneumatic tire according toa fifth embodiment;

FIG. 10B is a sectional view taken on line 10B-10B of FIG. 10A;

FIG. 11A is a plan view showing a tread of a pneumatic tire according toa sixth embodiment;

FIG. 11B is a sectional view taken on line 11B-11B of FIG. 11A;

FIG. 11C is a sectional view taken on line 11C-11C of FIG. 11A;

FIG. 12A is a plan view showing a tread of a pneumatic tire according toa seventh embodiment;

FIG. 12B is a sectional view taken on line 12B-12B of FIG. 12A;

FIG. 12C is a sectional view taken on line 12C-12C of FIG. 12A;

FIG. 13A is a plan view showing a tread of a pneumatic tire according toan eighth embodiment;

FIG. 13B is a sectional view taken on line 13B-13B of FIG. 13A;

FIG. 13C is a sectional view taken on line 13C-13C of FIG. 13A;

FIG. 14A is a plan view showing a tread of a pneumatic tire according toa ninth embodiment;

FIG. 14B is a sectional view taken on line 14B-14B of FIG. 14A;

FIG. 15A is a plan view showing a tread of a pneumatic tire according toa tenth embodiment;

FIG. 15B is a sectional view taken on line 15B-15B of FIG. 15A;

FIG. 16 is a plan view showing a tread of a conventional pneumatic tire;

FIG. 17 is a plan view showing a tread of another conventional pneumatictire;

FIG. 18A is a plan view showing a tread of still another conventionalpneumatic tire; and

FIG. 18B is a sectional view taken on line 18B-18B of FIG. 18A.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

A first embodiment of a pneumatic tire of the invention will bedescribed in detail with reference to the drawings.

As shown in FIG. 1, a circumferential wide major groove 14 is formed ona tire equatorial plane CL in a tread 12 of a pneumatic tire 10 of thefirst embodiment. The circumferential wide major groove 14 is linearlyextended in a tire circumferential direction (directions of arrows A andB, the direction of arrow B is a tire rotating direction). First narrowcircumferential minor grooves 16 extended in the tire circumferentialdirection are formed on the outside in a tire axis direction withrespect to the circumferential wide major groove 14. Second narrowcircumferential minor grooves 18 extended in the tire circumferentialdirection are further formed on the outside in the tire axis directionwith respect to the first narrow circumferential minor grooves 16.

As shown in FIG. 2A, a groove wall 16A on the side of the tireequatorial plane CL of the first narrow circumferential minor groove 16is linearly extended in the tire circumferential direction. In a groovewall 16B on the outside in the tire axis direction of the first narrowcircumferential minor groove 16, an inclination angle of the groove wall16B with respect to the tire circumferential direction is increased froma stepping-on side toward a kickout side such that a distance (groovewidth) with the groove wall 16A is widened.

As shown in FIG. 2B, in the groove wall 16A on the side of the tireequatorial plane CL of the first narrow circumferential minor groove 16,it is preferable that a groove wall angle θ_(16A) with respect to anormal HL to a wheel tread 12A of the tread 12 range from 40 degrees to80 degrees. In the first embodiment, the groove wall angle θ_(16A) isset at 60 degrees.

In the first narrow circumferential minor groove 16, a groove wall angleθ_(16B) of the groove wall 16B with respect to the normal HL is set at 5degrees.

As shown in FIGS. 2A and 2C, the groove wall 16A is in contact with thegroove wall 16B in the area of a substantially central portion to thestepping-on side of the first narrow circumferential minor groove 16. Asshown in FIG. 2C, a groove shape in cross section has a substantialV-shape in a portion where the groove wall 16A is in contact with thegroove wall 16B.

In the first narrow circumferential minor groove 16 shown in FIGS. 2Aand 2B, the portion where groove wall 16A is not in contact with thegroove wall 16B exhibits a reversal trapezoid while having a flat groovebottom 16C. The flat groove bottom 16C is parallel to the wheel tread12A of the tread 12 and is provided between a lower end of the groovewall 16A and a lower end of the groove wall 16B as shown in FIG. 2B.

The groove depth is increased toward the kickout side (direction ofarrow A) in the portion where the groove wall 16A and groove wall 16B ofthe first narrow circumferential minor groove 16 are in contact witheach other.

As shown in FIG. 1, the second narrow circumferential minor grooves 18is inclined with respect to the tire circumferential direction so as tosequentially come into contact with the road surface from the side ofthe tire equatorial plane CL toward the tread end 12E during an on-loadrotating operation.

As shown in FIG. 2A, in the second narrow circumferential minor groove18, an angle (inclination angle α) of the groove wall 18A on the side ofthe tire equatorial plane CL with respect to the tire circumferentialdirection is kept constant over the entire length. On the other hand, inthe groove wall 18B on the outside in the tire axis direction, an anglewith respect to the tire circumferential direction is increased towardthe kickout side.

In the groove wall 18A of the second narrow circumferential minor groove18, it is preferable that the inclination angle α range from 3 degreesto 20 degrees.

As shown in FIG. 2D, as with the first narrow circumferential minorgroove 16, in the second narrow circumferential minor groove 18, it ispreferable that the angle θ_(18A) of the groove wall 18A with respect tothe normal HL to the wheel tread 12A range from 40 degrees to 80degrees. In the first embodiment, the groove wall angle θ_(18A) is setat 60 degrees.

In the groove wall 18B of the second narrow circumferential minor groove18, the groove wall angle θ_(18B) with respect to the normal HL is setat 5 degrees.

As shown in FIGS. 2A and 2E, as with the first narrow circumferentialminor groove 16, the groove wall 18A is in contact with the opposinggroove wall 18B in the range of the substantial central portion to thestepping-on side of the second narrow circumferential minor groove 18.As with the first narrow circumferential minor groove 16, the grooveshape in cross section has a substantial V-shape in a portion where thegroove wall 18A is in contact with the groove wall 18B.

As shown in FIGS. 2A and 2D, in the second narrow circumferential minorgroove 18, the portion where the groove wall 18A is not in contact withthe groove wall 18B exhibits a flat groove bottom. The flat groovebottom is parallel to the wheel tread 12A of the tread 12 and isprovided between a lower end of the groove wall 18A and a lower end ofthe groove wall 18B.

As with the first narrow circumferential minor groove 16, in the secondnarrow circumferential minor groove 18, the groove depth is increasedtoward the kickout side in the area where the groove wall 18A and groovewall 18B are in contact with each other.

That is, in both the first narrow circumferential minor groove 16 andthe second narrow circumferential minor groove 18, the kick-out side islarger than the step-in side in the groove width and the groove depth.

As shown in FIG. 1, first transverse grooves 20, second transversegrooves 22, and third transverse grooves 24 are formed in the tread 12.The first transverse groove 20 is extended from the tread end 12E towardthe tire equatorial plane CL, and the first transverse groove 20 iscoupled to the circumferential wide major groove 14 while intersectingwith the first narrow circumferential minor groove 16 and the secondnarrow circumferential minor groove 18. The second transverse groove 22is arranged between the first transverse grooves 20, and the secondtransverse groove 22 is extended from the tread end 12E toward the tireequatorial plane CL. The second transverse groove 22 intersects with thefirst narrow circumferential minor groove 16 and the second narrowcircumferential minor groove 18, and the second transverse groove 22 isterminated without coupling to the circumferential wide major groove 14.The third transverse groove 24 is arranged between the first transversegroove 20 and the second transverse groove 22, the third transversegroove 24 is extended from the tread end 12E toward the tire equatorialplane CL, and the third transverse groove 24 is terminated between thefirst narrow circumferential minor groove 16 and the second narrowcircumferential minor groove 18.

The first transverse grooves 20, the second transverse grooves 22, andthe third transverse grooves 24 are inclined with respect to the tirecircumferential direction so as to sequentially come into contact withthe road surface from the side of the tire equatorial plane CL towardthe tread end 12E during the on-load rotating operation.

The tread 12 is zoned into a first block 26, a second block 28, astepping-on-side third block 30, and a kickout-side third block 32. Thefirst blocks 26 are zoned on both sides of the circumferential widemajor groove 14 in the tire axis direction by the circumferential widemajor groove 14, the first narrow circumferential minor groove 16, thefirst transverse groove 20, and the second transverse groove 22. Thesecond block 28 is zoned on the outside of the first block 26 in thetire axis direction by the first narrow circumferential minor groove 16,the second narrow circumferential minor groove 18, the first transversegroove 20, the second transverse groove 22, and the third transversegroove 24. The stepping-on-side third block 30 and the kickout-sidethird block 32 are located on the outside of the second block 28 in thetire axis direction. The stepping-on-side third block 30 is zoned by thesecond narrow circumferential minor groove 18, the first transversegroove 20, and the third transverse groove 24. The kickout-side thirdblock 32 is zoned by the second narrow circumferential minor groove 18,the second transverse groove 22, and the third transverse groove 24.

A tire equatorial plane-side end portion of the second transverse groove22 is terminated at a central portion of the first block 26 in the tireaxis direction, and a tire equatorial plane-side end portion of thethird transverse groove 24 is terminated at a central portion of thesecond block 28 in the tire axis direction.

At this point, assuming that W2 is the groove width of the firsttransverse groove 20, W3 is the groove width of the second transversegroove 22, and W4 is the groove width of the third transverse groove 24,preferably W3 is set in the range of 60% to 110% of W2 while W4 is setin the range of 20% to 60% of W2.

In the first embodiment, the groove width W3 of the second transversegroove 22 is set in the range of 64 to 100% of the groove width W2 ofthe first transverse groove 20, and the groove width W4 of the thirdtransverse groove 24 is set in the range of 28 to 42% of the groovewidth W2 of the first transverse groove 20.

A first transverse siping 34 is formed in a circumferential centralportion of the first block 26, and the first transverse siping 34couples the second transverse groove 22 and the circumferential widemajor groove 14. In the first block 26, a second transverse siping 36 isalso formed between the first transverse siping 34 and the firsttransverse groove 20, and the second transverse siping 36 couples thefirst narrow circumferential minor groove 16 and the circumferentialwide major groove 14.

Longitudinal sipings 38 are formed in the stepping-on-side third block30 and the kickout-side third block 32 respectively. The longitudinalsiping 38 is extended from a kickout edge toward the stepping-on side,and the longitudinal siping 38 is terminated at a block central portion.

(Action)

The tread pattern of the pneumatic tire 10 of the first embodiment isformed in a directional pattern. Therefore, in the wet road surfacedriving, the water between the pneumatic tire 10 and the road surfaceflows efficiently into the circumferential wide major groove 14, thefirst narrow circumferential minor groove 16, the second narrowcircumferential minor groove 18, the first transverse groove 20, thesecond transverse groove 22, and the third transverse groove 24, and thehigh wet performance is obtained while the increase in negative ratio issuppressed. Because the high wet performance is obtained while theincrease in negative ratio is suppressed, the wheel tread area can besecured in each block to increase the wear-resistant property.

A circumferential length of the second block 28 becomes a substantialhalf of the first block 26, and each of the circumferential lengths ofthe stepping-on-side third block 30 and kickout side third block 32becomes a substantial half of the second block 28. Therefore, the wetdrainage property can be improved on both the sides of the tread whilethe block rigidity can be increased on the tread central region toimprove the traction performance, brake performance, and corneringperformance. Furthermore, when the pneumatic tire 10 of the firstembodiment is used in a front wheel, the handling performance isimproved by increasing the block rigidity of the central region in thetire axis direction.

In the range where the block is zoned by the first narrowcircumferential minor groove 16 and the second narrow circumferentialminor groove 18, the widths and the depths of the first and secondnarrow circumferential minor grooves 16 and 18 are decreased from thekickout side toward the stepping-on side of the block during the on-loadrotating operation. Therefore, the block rigidity of the stepping-onside is increased to improve the traction performance, brakeperformance, and cornering performance in the block adjacent to thefirst narrow circumferential minor groove 16 and the second narrowcircumferential minor groove 18.

The tire equatorial plane-side terminal position of the secondtransverse groove 22 is located at the central region of the first block26 in the tire axis direction, and the tire equatorial plane-sideterminal position of the third transverse groove 24 is located at thecentral region of the second block 28 in the tire axis direction.Therefore, the water existing on the wheel tread of each block canefficiently be drained, and the block wheel tread area (related towear-resistant property) and the block rigidity (related to roadholdingability) can be secured while the high wet drainage performance isobtained. Accordingly, the high wet drainage performance, roadholdingability, and wear-resistant property can be obtained in a preferablemanner.

The groove wall 16A on the side of the tire equatorial plane CL of thefirst narrow circumferential minor groove 16 is linearly extended in thetire circumferential direction, and the angle θ_(16A) with respect tothe normal to the wheel tread 12A is set in the range of 50 degrees to80 degrees. Therefore, a balance can be achieved between the rigidity ofthe first block 26 that is provided at the tire equatorial plane CL sidewith respect to the first narrow circumferential minor groove 16 and thewet drainage property of the first narrow circumferential minor groove16.

At the block stepping-on side of the first narrow circumferential minorgroove 16, the groove wall 16A at the side of the tire equatorial planeCL is coupled to the opposing groove wall 16B at the outside in the tireaxis direction. Therefore, the rigidity can be enhanced to improve thetraction performance, brake performance, and cornering performance inthe second block 28 that is provided at the outside of the first narrowcircumferential minor groove 16 in the tire axis direction.

Similarly, at the block stepping-on side of the second narrowcircumferential minor groove 18, the groove wall 18A on the side of thetire equatorial plane CL is coupled to the opposing groove wall 18B onthe outside in the tire axis direction. Therefore, the rigidity can beenhanced in the third block 30 that is provided at the outside of thesecond narrow circumferential minor groove 18 in the tire axisdirection.

The groove width W3 of the second transverse groove 22 is set in therange of 60% to 110% of the groove width W2 of the first transversegroove 20, and the groove width W4 of the third transverse groove 24 isset in the range of 20% to 60% of the groove width W2 of the firsttransverse groove 20. Therefore, a balance can be achieved between thewet drainage property and the block rigidity in the region surrounded bythe first transverse groove 20 and the second transverse groove 22.

The groove width W3 of the second transverse groove 22 is setsubstantially equal to the groove width W2 of the first transversegroove 20, namely, the groove width W3 of the second transverse groove22 is set in the range of 60% to 110% of the groove width W2 of thefirst transverse groove 20, which secures the high wet drainageproperty.

The second narrow circumferential minor groove 18 arranged in theoutermost side in the tire axis direction is inclined so as sequentiallycome into contact with the road surface from the side of the tireequatorial plane CL toward the tread end 12E during the on-load rotatingoperation. Therefore, the wet drainage performance is improved near boththe outsides in the tire axis direction of the tire ground contactsurface portion.

Accordingly the pneumatic tire 10 of the first embodiment is suitablefor the use of the racing ultra-high performance vehicle front-tire.

The wet drainage performance cannot be improved when the inclinationangle α is lower than three degrees in the groove wall 18A of the secondnarrow circumferential minor groove 18.

On the other hand, when the inclination angle α is more than 20 degrees,the block end at the kick-out side of the second block 28 that isadjacent to the second transverse groove 22 becomes an acute angle,which results in the undesirable shortage of the block rigidity.

Test Example

A tire of Conventional example and a tire of the present Example areattached to the front wheel of the actual vehicle, and a test isperformed to confirm the effect of the invention. In the test, the tireof Example is compared to the tire of Conventional example for thehydroplaning, wet circuit lap time, and wet grip.

Hydroplaning: the vehicle runs on the wet road surface whose water depthis 2 mm, and hydroplaning generation speed is measured. The evaluationis displayed as an index in which the hydroplaning generation speed isset at 100 in the conventional tire. As the index is increased, thehydroplaning generation speed is enhanced. Therefore, the higher indexindicates that the tire has the excellent wet drainage property.

Wet circuit lap time: a lap time is measured when the vehicle runs roundon the wet road surface (test course) whose water depth is 2 mm. Theevaluation is displayed as an index in which the lap time is set at 100in the conventional tire. As the index is decreased, the lap time isshortened. Therefore, the lower index indicates that the tire has theexcellent wet circuit running property.

Wet grip: a feeling evaluation is performed by a test driver when thevehicle runs round on the wet road surface (test course) whose waterdepth is 2 mm. The evaluation is displayed as an index in which thefeeling is set at 100 in the conventional tire. As the index isincreased, the tire has the excellent wet grip.

The tire of Example: the pneumatic tire of the above-described firstembodiment is used.

The tire of Conventional example: a pneumatic tire having a treadpattern shown in FIG. 16 is used.

As shown in FIG. 16, in a tread 502 of a pneumatic tire 500 ofConventional example, a circumferential wide major groove 504 is formedon the tire equatorial plane CL.

In the tread 502, plural first transverse grooves 506 are formed on bothsides of the circumferential wide major groove 504. The first transversegroove 506 is extended from a tread end 502E toward the circumferentialwide major groove 504, and the first transverse groove 506 is coupled tothe circumferential wide major groove 504. A second transverse groove508 is formed between the first transverse grooves 506. The secondtransverse groove 508 is extended from the tread end 502E toward thecircumferential wide major groove 504, and the second transverse groove508 is terminated at a middle portion between the tire equatorial planeCL and the tread end 502E.

A minor groove 510 is coupled to the middle portion of the firsttransverse groove 506. The minor groove 510 is extended toward thestepping-on side and the minor groove 510 is terminated in the block.

Sizes are RAR 265/55R13 (tread width is 200 mm) in the tires ofConventional example and Example. Table 1 shows specifications of eachtire.

Test vehicle wheel alignment:

-   -   front-wheel toe angle (toe-out side) of 1 mm and negative camber        angle of 4°, rear-wheel toe angle (toe-in side) of 1 mm and        negative camber angle of 3° Table 2 shows the test results.

TABLE 1 Conventional example Example Circumferential wide major groove:2.8 2.8 groove depth D0 (mm) Circumferential wide major groove: 13 13groove width W0 (mm) First and second narrow circumferential — 1.3 to2.8 minor grooves: groove depth D1 (mm) First and second narrowcircumferential — 4.0 minor grooves: groove width W1 (mm) of middleportion Circumferential inclination angle α — 8 (degree) to tireequatorial plane-side groove wall of second narrow circumferential minorgroove First transverse groove: groove depth D2 2.8 2.8 First transversegroove: groove width W2 12 to 20 14 to 19 Second transverse groove:groove depth D3 — 2.8 Second transverse groove: groove width W3 —  9 to19 Third transverse groove: groove depth D4 2.8 2.8 Third transversegroove: groove width W4 6 to 9 4 to 8

TABLE 2 Conventional Name example Example Hydroplaning 100 110 Wetcircuit lap time 100 96 Wet grip 100 120

As can be seen from the test results, in the pneumatic tire of Exampleto which the invention is applied, all the hydroplaning, wet circuit laptime, and wet grip are improved compared with the pneumatic tire ofConventional example.

Second Embodiment

A second embodiment of a pneumatic tire of the invention will bedescribed in detail with reference to the drawings.

As shown in FIG. 3, a circumferential wide major groove 114 is formed onthe tire equatorial plane CL in a tread 112 of a pneumatic tire 110 ofthe second embodiment. The circumferential wide major groove 114 islinearly extended in the tire circumferential direction. First narrowcircumferential minor grooves 116 extended in the tire circumferentialdirection are formed on the outside of the circumferential wide majorgroove 114 in a tire axis direction. Second narrow circumferential minorgrooves 118 extended in the tire circumferential direction are furtherformed on the outside of the first narrow circumferential minor grooves116 in the tire axis direction.

As shown in FIG. 4A, a groove wall 116A of the first narrowcircumferential minor groove 116 that is provided at the tire equatorialplane CL side is linearly extended in the tire circumferentialdirection. In a groove wall 116B of the first narrow circumferentialminor groove 116 provided at the outside in the tire axis direction, theinclination angle of the groove wall 116B with respect to the tirecircumferential direction is increased from the stepping-on side towardthe kickout side such that a distance (groove width) formed between thegroove wall 116A and the groove wall 116B is widened.

As shown in FIG. 4B, in the groove wall 116A, it is preferable that thegroove wall angle θ_(16A) with respect to the normal HL to a wheel tread112A of the tread 112 range from 50 degrees to 80 degrees. In the secondembodiment, the groove wall angle θ_(16A) is set at 60 degrees.

In the first narrow circumferential minor groove 116, the groove wallangle θ_(16B) of the groove wall 116B is set at 5 degrees.

As shown in FIGS. 4A and 4C, the groove wall 116A is in contact with thegroove wall 116B in the area of the substantially central portion to thestepping-on side of the first narrow circumferential minor groove 116.As shown in FIG. 4C, the groove shape in cross section has thesubstantial V-shape in a portion where the groove wall 116A is incontact with the groove wall 116B.

In the first narrow circumferential minor groove 116 shown in FIGS. 4Aand 4B, the portion where groove wall 116A is not in contact with thegroove wall 116B exhibits a reversal trapezoid while having a flatgroove bottom 116C. The flat groove bottom 116C is parallel to the wheeltread 112A of the tread 112 and is provided between a lower end of thegroove wall 116A and a lower end of the groove wall 116B as shown inFIG. 4B.

The groove depth is increased toward the kickout side in the portionwhere the groove wall 116A and groove wall 116B are in contact with eachother in the first narrow circumferential minor groove 116.

As shown in FIG. 4A, as with the groove wall 116A of the first narrowcircumferential minor groove 116, a groove wall 118A at the tireequatorial plane CL side of a second narrow circumferential minor groove118 is linearly extended in the tire circumferential direction. In thegroove wall 118B provided at the outside of the second narrowcircumferential minor groove 118 in the tire axis direction, theinclination angle with respect to the tire circumferential direction isincreased from the stepping-on side toward the kickout side such thatthe distance (groove width) formed between the groove wall 118A and thegroove wall 118B is widened.

As shown in FIG. 4D, as with the first narrow circumferential minorgroove 116, in the second narrow circumferential minor groove 118, it ispreferable that in the groove wall 118A, the angle θ_(18A) with respectto the normal HL to the wheel tread 112A range from 50 degrees to 80degrees. In the second embodiment, the groove wall angle θ_(18A) is setat 60 degrees.

In the groove wall 118B of the second narrow circumferential minorgroove 118, the groove wall angle θ_(18B) is set at 5 degrees.

As shown in FIGS. 4A and 4D, as with the first narrow circumferentialminor groove 116, the groove wall 118A is in contact with the opposinggroove wall 118B in the area of the substantial central portion to thestepping-on side in the second narrow circumferential minor groove 118.As with the first narrow circumferential minor groove 116, the grooveshape in cross section has the substantial V-shape in the portion wherethe groove wall 118A is in contact with the groove wall 118B.

As shown in FIGS. 4A and 4E, as with the first narrow circumferentialminor groove 116, in the second narrow circumferential minor groove 118,the portion where groove wall 118A is not in contact with the groovewall 118B has the flat groove bottom that is parallel to the wheel tread112A of the tread 112. The flat groove bottom is formed between thelower end of the groove wall 118A and the lower end of the groove wall118B.

As with the first narrow circumferential minor groove 116, the groovedepth is increased toward the kickout side in the portion where thegroove wall 118A and groove wall 118B are in contact with each other inthe second narrow circumferential minor groove 118.

That is, in both the first narrow circumferential minor groove 116 andthe second narrow circumferential minor groove 118, the stepping-on sideis larger than the kickout side in the groove width and the groovedepth. Therefore, the block rigidity is secured while the drainageproperty is improved.

As shown in FIG. 3, first transverse grooves 120 and second transversegrooves 122 are formed in the tread 112. The first transverse groove 120is extended from the tread end 112E toward the tire equatorial plane CL,and the first transverse groove 120 is coupled to the circumferentialwide major groove 114 while intersecting with the first narrowcircumferential minor groove 116 and the second narrow circumferentialminor groove 118. The second transverse groove 122 is arranged betweenthe first transverse grooves 120, and the second transverse groove 122is extended from the tread end 112E toward the tire equatorial plane CL.The second transverse groove 122 intersects with the second narrowcircumferential minor groove 118, and the second transverse groove 122is terminated in the middle portion between the first narrowcircumferential minor groove 116 and the second narrow circumferentialminor groove 118.

The tread 112 is zoned into a first block 126, a second block 128, astepping-on-side third block 130, and a kickout-side third block 132. Onboth sides of the circumferential wide major groove 114 in the tire axisdirection, the first blocks 126 are zoned by the circumferential widemajor groove 114, the first narrow circumferential minor groove 116, andthe first transverse groove 120. The second block 128 is zoned at theoutside of the first block 126 in the tire axis direction by the firstnarrow circumferential minor groove 116, the second narrowcircumferential minor groove 118, the first transverse groove 120, andthe second transverse groove 122. The stepping-on-side third block 130and the kickout-side third block 132 are located at the outside of thesecond block 128 in the tire axis direction while zoned by the secondnarrow circumferential minor groove 118, the first transverse groove120, and the second transverse groove 122.

The first transverse groove 120 has a bottom raising portion 140 at theside of the circumferential wide major groove 114.

As shown in FIGS. 3 and 5, the bottom raising portion 140 of the secondembodiment is formed from an end portion of the first transverse groove120 that is provided at the side of the circumferential wide majorgroove 114 to the outside in the tire axis direction. Accordingly, thegroove wall of the circumferential wide major groove 114 is linearlyextended along the tire circumferential direction, and there is noirregularity in the groove wall.

In the bottom raising portion 140, the end portion at the side of thecircumferential wide major groove 14 is highest and the height isgradually decreased toward the outside in the tire axis direction. Asshown in FIG. 5, the sectional shape in a longitudinal direction (thetire width direction) exhibits a substantial triangle.

As shown in FIG. 3, in the second embodiment, a top portion 140A of thebottom raising portion 140 is linearly arranged at an extended line of awheel tread opening edge portion of the circumferential wide majorgroove 114.

As shown in FIG. 3, in the second embodiment, a base 140B of the bottomraising portion 140 is linearly formed in the tire circumferentialdirection (parallel to top portion 140A).

As shown in FIG. 3, in the bottom raising portion 140, it is preferablethat a size in tire axis direction L0 be in the range of 60 to 200% of agroove width size W0 of the circumferential wide major groove 114. Inthe second embodiment, the size in tire axis direction L0 is set at 123%of the groove width size W0.

As shown in FIG. 5A, in the bottom raising portion 140 of the secondembodiment, the top portion 140A becomes a vertex of the triangle, andthe top portion 140A has no width when viewed from a cross section inthe longitudinal direction (the tire width direction). Alternatively, asshown in FIGS. 5B and 6, the top portion 140A may have a width L1.

However, the width L1 of the top portion 140A is set to 3 mm or lesswhen the position of the top portion 140A is flush with the wheel tread112A of the tread 112.

As shown in FIG. 5C, a depth d at the top portion 140A is set to 10% ormore of a groove depth D (portion except for bottom raising portion 140,i.e., the deepest portion).

As shown in FIG. 3, a tire equatorial plane-side end portion of thesecond transverse groove 122 is terminated in the central portion of thesecond block 128 in the tire axis direction.

Preferably the groove width W3 of the second transverse groove 122 isset in the range of 10 to 80% of the groove width W2 of the firsttransverse groove 120. The groove width W3 of the second transversegroove 122 of the second embodiment is set in the range of 14 to 50% ofthe groove width W2 of the first transverse groove 120.

A transverse siping 134 is formed in the central portion of the firstblock 126 in the circumferential direction. The transverse siping 134 isextended from the first narrow circumferential minor groove 116 towardthe block central, and the transverse siping 134 is terminated in theblock central portion.

Longitudinal sipings 138 are formed in the central portion of thestepping-on-side third block 130 in the tire axis direction and thecentral portion of the kickout-side third block 132 in the tire axisdirection respectively. The longitudinal siping 138 is extended fromkickout edge toward the stepping-on side, and the longitudinal sipings138 is terminated in the block central portion.

(Function)

In the pneumatic tire 110 of the second embodiment, when the vehicleruns on the wet road surface, the water near the central portion in thetire axis direction flows into the circumferential wide major groove114, and other water flows into the first transverse groove 120.

The water on the wheel tread of the block surrounded by thecircumferential wide major groove 114 and the first transverse groove120 flows into the circumferential wide major groove 114, the firstnarrow circumferential minor groove 116, and the second transversegroove 122.

The tread pattern of the pneumatic tire 110 is formed in a directionalpattern. Therefore, when the vehicle runs on the wet road surface, thewater between the pneumatic tire 110 and the road surface flowsefficiently into the circumferential wide major groove 114, the firstnarrow circumferential minor groove 116, the second narrowcircumferential minor groove 118, the first transverse groove 120, andthe second transverse groove 122, and the high wet performance isobtained while the increase in negative ratio is suppressed.

Because the high wet performance is obtained while the increase innegative ratio is suppressed, the wheel tread area can be secured ineach block to improve the wear-resistant property.

In the area where the block is zoned by the first narrow circumferentialminor groove 116 and the second narrow circumferential minor groove 118,the widths and the depths of the first and second narrow circumferentialminor grooves 116 and 118 are decreased from the kickout side toward thestepping-on side of the block that are defined during the on-loadrotating operation. Therefore, the block rigidity on the stepping-onside is increased to improve the traction performance, brakeperformance, and cornering performance in the block adjacent to thefirst narrow circumferential minor groove 116 and the second narrowcircumferential minor groove 118.

The groove wall 116A that is provided at the side of the tire equatorialplane CL in the first narrow circumferential minor groove 116 islinearly extended in the tire circumferential direction, and the angleθ_(16A) with respect to the normal to the wheel tread 112A is set in therange of 50 degrees to 80 degrees. Therefore, a balance can be achievedbetween the rigidity of the first block 126 at the side of the tireequatorial plane CL with respect to the first narrow circumferentialminor groove 116 and the wet drainage property of the first narrowcircumferential minor groove 116.

At the block stepping-on side of the first narrow circumferential minorgroove 116, the groove wall 116A is coupled to the opposing groove wall116B that is provided at the outside in the tire axis direction.Therefore, the rigidity can be enhanced to improve the tractionperformance, brake performance, and cornering performance in the secondblock 128 that is provided at the outside of the first narrowcircumferential minor groove 116 in the tire axis direction.

Similarly, at the block stepping-on side of the second narrowcircumferential minor groove 118, the groove wall 118A provided at theside of the tire equatorial plane CL is coupled to the opposing groovewall 118B provided at the outside in the tire axis direction. Therefore,the rigidity can be enhanced in the third block 130 that is provided atthe outside of the second narrow circumferential minor groove 118 in thetire axis direction.

The groove width of the second transverse groove 122 is set in the rangeof 10% to 80% of the groove width of the first transverse groove 120.Therefore, a balance can achieved between the wet drainage property andthe block rigidity in the region at the outside in the tire axisdirection of the tread 112.

Accordingly the pneumatic tire 110 of the second embodiment is suitablefor the use of the racing ultra-high performance vehicle rear-tire.

Test Example

The tire of Conventional example and the tires of the present Examplesto which the invention is applied are attached to the rear wheel of theactual vehicle, and the test is performed to confirm the effect of theinvention. In the test, the tires of Examples are compared to the tireof Conventional example for the hydroplaning, wet circuit lap time, andwet grip.

Hydroplaning: the vehicle runs on the wet road surface whose water depthis 2 mm, and hydroplaning generation speed is measured. The evaluationis displayed as an index in which the hydroplaning generation speed isset at 100 in the conventional tire. As the index is increased, thehydroplaning generation speed is enhanced. Therefore, the higher indexindicates that the tire has the excellent wet drainage property.

Wet circuit lap time: a lap time is measured when the vehicle runs roundon the wet road surface (test course) whose water depth is 2 mm. Theevaluation is displayed as an index in which the lap time is set at 100in the conventional tire. As the index is decreased, the lap time isshortened. Therefore, the lower index indicates that the tire has theexcellent wet circuit running property.

Wet grip: the feeling evaluation is performed by the test driver whenthe vehicle runs round on the wet road surface (test course) whose waterdepth is 2 mm. The evaluation is displayed as an index in which thefeeling is set at 100 in the conventional tire. As the index isincreased, the tire has the excellent wet grip.

The tire of Example 1: the pneumatic tire shown in FIG. 3 of the secondembodiment is used.

The tire of Example 2: the pneumatic tire shown in FIG. 6 of the secondembodiment is used. The top portion of the bottom raising portion hasthe width of 2 mm.

The tire of Conventional example: a pneumatic tire having a treadpattern shown in FIG. 17 is used.

As shown in FIG. 17, in a tread 602 of a pneumatic tire 600 ofConventional example, a circumferential wide major groove 604 is formedon the tire equatorial plane CL.

In the tread 602, plural first transverse grooves 606 are formed on bothsides of the circumferential wide major groove 604. The first transversegroove 606 is extended from a tread end 602E toward the circumferentialwide major groove 604, and the first transverse groove 606 is coupled tothe circumferential wide major groove 604. A second transverse groove608 is formed between the first transverse grooves 606. The secondtransverse groove 608 is extended from the tread end 602E toward thecircumferential wide major groove 604, and the second transverse groove608 is terminated at the middle portion between the tire equatorialplane CL and the tread end 602E.

A minor groove 610 is coupled to the middle portion of the firsttransverse groove 606. The minor groove 610 is extended toward thestepping-on side and the minor groove 610 is terminated in the blockcentral portion.

The numeral 612 designates siping formed in the land portion.

Sizes are RAR325/55R13 (tread width is 250 mm) in the tires ofConventional example and Examples. Table 3 shows specifications of eachtire.

Test vehicle wheel alignment: front-wheel toe angle (toe-out side) of 1mm and negative camber angle of 4°, rear-wheel toe angle (toe-in side)of 1 mm and negative camber angle of 3° Table 4 shows the test results.

TABLE 3 Conventional example Example 1 Example 2 Circumferential wide2.8 2.8 2.8 major groove Groove depth D0 (mm) Circumferential wide 17 1717 major groove Groove width W0 (mm) First and second — 1.3 to 2.8 1.3to 2.8 narrow circumferential minor grooves Groove depth D1 First andsecond — 4.0 4.0 narrow circumferential minor grooves Groove width W1(mm) of middle portion First transverse groove 2.8 2.8 2.8 Groove depthD2 (mm) First transverse groove 13 to 15 14 to 20 14 to 20 Groove widthW2 (mm) Second transverse 2.8 2.8 2.8 groove Groove depth D3 (mm) Secondtransverse 6 to 9 2 to 10 2 to 10 groove Groove width W3 (mm) Bottomraising portion — 16 16 With L0 (mm) Bottom raising portion — 0 2 Topportion width L1 (mm)

TABLE 4 Conventional Name example Example 1 Example 2 Hydroplaning 100115 113 Wet circuit lap time 100 92 90 Wet grip 100 115 117

As can be seen from the test results, in the pneumatic tires of Examples1 and 2 to which the invention is applied, all the hydroplaning, wetcircuit lap time, and wet grip are improved compared with the pneumatictire of Conventional example.

Third Embodiment

A third embodiment of a pneumatic tire of the invention will bedescribed in detail with reference to the drawings.

As shown in FIG. 7, a pneumatic tire 210 according to the thirdembodiment includes a carcass 212. The carcass 212 includes cords whichare substantially extended in the radial direction, and both endportions are folded by bead cores 211 respectively. The carcass 212 isformed by a single layer or multilayer.

A belt layer 214 in which plural belt plies are laminated is embedded onthe outside in a tire radial direction of a crown portion 12C of thecarcass 212. A tread portion 218 in which the grooves are arranged isformed on the outside in the tire radial direction of the belt layer214.

As shown in FIG. 8A, in a wheel tread portion 219 of the tread portion218, a first outer major groove 222A extended in the tirecircumferential direction is formed on one surface side with respect tothe tire equatorial plane CL, and a second outer major groove 222Bextended in the tire circumferential direction is formed on the othersurface side with respect to the tire equatorial plane CL. Each of thefirst outer major groove 222A and the second outer major groove 222B isformed at the position which is close to a quarter point Q of a width Wof the wheel tread portion 219. The first outer major groove 222A andthe second outer major groove 222B zone the wheel tread portion 219 intoa central region 220 and side regions 221.

In both the side regions 221, lug grooves 226 are formed atsubstantially equal intervals in the tire circumferential direction, andthe tire equatorial plane-side end portion of the lug groove 226 issubstantially opened to and terminated in the first outer major groove222A or the second outer major groove 222B.

Both the end portions in the tire width direction of each lug groove 226are extended across the tread end such that the water can be drained tothe outside in the tire width direction. As used herein, the term “treadend” shall mean an outermost ground contact portion in the tire widthdirection, in the case where the pneumatic tire is attached to astandard rim defined by JATMA YEAR BOOK (2004, specification of THEJapan Automobile tire Manufacturers Association), the pneumatic tire isfilled with an inner pressure of 100% of a pneumatic pressure (maximumpneumatic pressure) corresponding to a maximum load capacity (bold loadin an inner pressure-load capacity corresponding table) in anapplication size and ply rating in JATMA YEAR BOOK, and the maximum loadcapacity is applied to the pneumatic tire. When TRA specification orETRTO specification is applied to a place where the pneumatic tire isused or a place where the pneumatic is manufactured, the test is subjectto each specification.

In the central region 220, a first inner major groove 224A extended inthe tire circumferential direction is formed on one side surface withrespect to the tire equatorial plane CL, and a second inner major groove224B extended in the tire circumferential direction is formed on theother surface with respect to the tire equatorial plane CL. Each of thefirst outer major groove 222A, second outer major groove 222B, firstinner major groove 224A, and second inner major groove 224B is the majorgroove having the groove depth D₀. The first inner major groove 224A andthe second inner major groove 224B are arranged at the positions suchthat a distance between the first inner major groove 224A and the secondinner major groove 224B, a distance between the first outer major groove222A and the first inner major groove 224A, and a distance between thesecond outer major groove 222B and the second inner major groove aresubstantially equalized to one another.

A central land portion row 228, a first adjacent land portion row 230,and a second adjacent land portion row 232 are formed in the centralregion 220. The central land portion row 228 is zoned by the first innermajor groove 224A and the second inner major groove 224B. The firstadjacent land portion row 230 is zoned by the first outer major groove222A and the first inner major groove 224A. The second adjacent landportion row 232 is zoned by the second outer major groove 222B and thesecond inner major groove 224B.

Plural central inclined grooves (lug grooves) 234 are formed in thecentral region 220. The central inclined grooves 234 are formed atsubstantially equal intervals so as to cross the central land portionrow 228, and the central inclined grooves 234 are extended whileinclined with respect to the tire circumferential direction. As aresult, a land portion 229 is formed in the central land portion row 228by the first inner major groove 224A, second inner major groove 224B,central inclined grooves 234 adjacent to each other in the tirecircumferential direction. The land portions 229 are arrayed in the tirecircumferential direction so as to stride over both the sides of thetire equatorial plane CL.

Plural first inclined grooves 236 are arranged in the central region220. The first inclined grooves 236 are formed at substantially equalintervals so as to cross the first adjacent land portion row 230, andthe first inclined grooves 236 are extended while inclined with respectto the tire circumferential direction. As a result, a land portion 231is formed in the first adjacent land portion row 230 by the first innermajor groove 224A, first outer major groove 222A, first inclined grooves236 adjacent to each other in the tire circumferential direction. Theland portions 231 are arrayed in the tire circumferential direction. Theinclination direction of the first inclined groove 236 is opposite tothe inclination direction of the central inclined groove 234.

Similarly, plural second inclined grooves 238 are arranged in thecentral region 220. The second inclined grooves 238 are formed atsubstantially equal intervals so as to cross the second adjacent landportion row 232, and the second inclined grooves 238 are extended whileinclined with respect to the tire circumferential direction. As aresult, a land portion 233 is formed in the second adjacent land portionrow 232 by the second inner major groove 224B, second outer major groove222B, second inclined grooves 238 adjacent to each other in the tirecircumferential direction. The land portions 233 are arrayed in the tirecircumferential direction. The inclination direction of the secondinclined groove 238 is similar to the inclination direction of the firstinclined groove 236.

The groove length is set at L₀ for each of the central inclined groove234, first inclined groove 236, and second inclined groove 238. Thegroove depth is set at D₁ (see FIG. 8B) in the groove portion except forthe later-mentioned bottom raising portion for each of the centralinclined groove 234, first inclined groove 236, and second inclinedgroove 238.

(First Inclined Groove)

A first bottom raising portion 242 which raises the groove bottom isformed near a first inner major groove-side end 236J in the firstinclined groove 236, so that the first inclined groove 236 issubstantially opened to and terminated in the first inner major groove224A (also see FIG. 8B).

A cross section of the first bottom raising portion 242 in the tirewidth direction (longitudinal direction of the groove) is formed in achevron shape, the first inner major groove-side end 236J has thehighest peak where a first edge line 244 is formed, and a first inclinedsurface 246 is formed as the groove bottom surface. In the first bottomraising portion 242, the groove depth is gradually increased from thefirst inner major groove-side end 236J toward a first outer majorgroove-side end 242K at the bottom raising portion 242 (namely, thegroove depth is gradually decreased from the first outer majorgroove-side end 242K of the first bottom raising portion 242 toward thefirst inner major groove-side end 236J).

The first inclined groove 236 is completely opened to the first outermajor groove 222A at the first outer major groove-side end 236K of thefirst inclined groove 236.

A groove length L₁ of a groove portion 236P in which the first inclinedsurface 246 is formed as the groove bottom surface is set in the rangeof 5 to 100% of the groove length L₀ of the first inclined groove 236having the groove portion 236P.

The position of the first edge line 244 in the tire width direction islocated at the same position as the groove edge of the first inner majorgroove 224A.

(Central Inclined Groove)

A central bottom raising portion 252 which raises the groove bottom isformed near a first inner major groove-side end 234J of the centralinclined groove 234, so that the central inclined groove 234 issubstantially opened to and terminated in the first inner major groove224A.

As with the first bottom raising portion 242, a cross section in thetire width direction (longitudinal direction of the groove) of thecentral bottom raising portion 252 is formed in a chevron shape, thefirst inner major groove-side end 234J has the highest peak where acentral edge line 254 is formed, and a central inclined surface 256 isformed as the groove bottom surface. In the central bottom raisingportion 252, the groove depth is gradually increased from the firstinner major groove-side end 234J toward a second inner major groove-sideend 252K at the central bottom raising portion 252 (namely, the groovedepth is gradually decreased from the second inner major groove-side end252K of the central bottom raising portion 252 toward the first innermajor groove-side end 234J).

The central inclined groove 234 is completely opened to the second innermajor groove 224B at the second inner major groove-side end 234K of thecentral inclined groove 234.

The groove length of a groove portion 234P in which the central inclinedsurface 256 is formed as the groove bottom surface is set in the rangeof 5 to 100% of the groove length of the central inclined groove 234having the groove portion 234P.

The position of the central edge line 254 in the tire width direction islocated at the same position as the groove edge of the first inner majorgroove 224A.

(Second Inclined Groove)

A second bottom raising portion 262 which raises the groove bottom isformed near a second inner major groove-side end 238J of the secondinclined groove 238, so that the second inclined groove 238 issubstantially opened to and terminated in the second inner major groove224B.

As with the central bottom raising portion 252, a cross section in thetire width direction (longitudinal direction of the groove) of thesecond bottom raising portion 262 is formed in a chevron shape, thesecond inner major groove-side end 238J has the highest peak where asecond edge line 264 is formed, and a second inclined surface 266 isformed as the groove bottom surface. In the second bottom raisingportion 262, the groove depth is gradually increased from the secondinner major groove-side end 238J toward a second outer major groove-sideend 262K at the second bottom raising portion 262 (namely, the groovedepth is gradually decreased from the second outer major groove-side end262K toward the second inner major groove-side end 238J at the secondbottom raising portion 262).

The second inclined groove 238 is completely opened to the second outermajor groove 222B at the second outer major groove-side end 238Kthereof.

The groove length of a groove portion 238P in which the second inclinedsurface 266 is formed as the groove bottom surface is set in the rangeof 5 to 100% of the groove length of the second inclined groove 238having the groove portion 238P.

The position of the second edge line 264 in the tire width direction islocated at the same position as the groove edge of the second innermajor groove 224B.

(Lug Groove)

The lug grooves 226 have the same basic configuration, action, andeffect on both the sides of the tire equatorial plane CL. Therefore, thelug groove 226 indicated on the left of FIG. 8A (one surface side of thetire equatorial plane CL) will be described, and the description will beomitted for the lug groove 226 on the right.

A lug groove bottom raising portion 272 which raises the groove bottomis formed near a first outer major groove-side end 226J of the luggroove 226, so that the lug groove 226 is substantially opened to andterminated in the first outer major groove 222A (also see FIG. 8B).

A cross section of the lug groove bottom raising portion 272 in the tirewidth direction (longitudinal direction of the groove) is formed in achevron shape, the first outer major groove-side end 226J has thehighest peak where a lug groove edge line 274 is formed, and a luggroove inclined surface 276 is formed as the groove bottom surface. Inthe lug groove bottom raising portion 272, the groove depth is graduallyincreased from the first outer major groove-side end 226J toward a treadend-side end 272K at the lug groove bottom raising portion 272 (namely,the groove depth is gradually decreased from the tread end-side end 272Ktoward the first outer major groove-side end 226J at the lug groovebottom raising portion 272).

The lug groove 226 is completely opened at a tread end T.

The groove length of a groove portion 226P in which the lug grooveinclined surface 276 is formed as the groove bottom surface is set inthe range of 5 to 100% of the groove length of the lug groove 226 havingthe groove portion 226P.

The position of the lug groove edge line 274 in the tire width directionis located at the same position as the groove edge of the first outermajor groove 222A.

The respective length of the groove portion where the groove bottom isformed is set at L₁ (see FIG. 8B) for each of the central inclinedsurface 256, first inclined surface 246, second inclined surface 266,and the lug groove inclined surface 276.

(Function)

As described above, in the third embodiment, the directional treadpattern is formed in the wheel tread portion 219, and the central bottomraising portion 252, first bottom raising portion 242, second bottomraising portion 262, and lug groove bottom raising portion 272 areformed in the central inclined groove 234, first inclined groove 236,second inclined groove 238, and lug groove 226 respectively.

Therefore, in wet road surface driving, the water near the centralbottom raising portion 252 is distributed into the water which flowsinto the first inner major groove 224A while not guided by the centralinclined surface 256 and the water which flows into the second innermajor groove 224B while guided by the central inclined surface 256. Thewater near the first bottom raising portion 242 is distributed into thewater which flows into the first inner major groove 224A while notguided by the first inclined surface 246 and the water which flows intothe first outer major groove 222A while guided by the first inclinedsurface 246. The water near the second bottom raising portion 262 isdistributed into the water which flows into the second inner majorgroove 224B while not guided by the second inclined surface 266 and thewater which flows into the second outer major groove 222B while guidedby the second inclined surface 266. The water near the lug groove bottomraising portion 272 is distributed into the water which flows into thefirst outer major groove 222A while not guided by the lug grooveinclined surface 276 and the water which flows into the tread end Twhile guided by the lug groove inclined surface 276. Accordingly, thepneumatic tire having the excellent wet drainage property is obtained.

The roadholding ability on the dry road surface, uneven wear-resistantproperty, and pattern noise property are improved, because the rigidityis enhanced in the corner portion (particularly, the corner portion 231Cwhich has an acute angle when viewed from the side of the wheel treadportion 219) of the adjacent land portion 231 with the provision of thefirst bottom raising portion 242. The same effect can be obtained incorner portions of land portions adjacent to the central bottom raisingportion 252, the second bottom raising portion 262 and lug groove bottomraising portion 272.

Fourth Embodiment

Then, a fourth embodiment will be described with reference to FIG. 9A.In a pneumatic tire according to the fourth embodiment, when comparedwith the third embodiment, a first outer major groove 322A is formed inplace of the first outer major groove 222A, a second outer major groove322B is formed in place of the second outer major groove 222B, a firstinner major groove 324A is formed in place of the first inner majorgroove 224A, and a second inner major groove 324B is formed in place ofthe second inner major groove 224B. Instead of the lug grooves 226, alug groove 326 is formed on one surface side of the tire equatorialplane CL, and a lug groove 327 is formed on the other surface side ofthe tire equatorial plane CL. The basic configuration, function, andeffect of a second inclined groove 338 are similar to those of a firstinclined groove 336, so that the description of the second inclinedgroove 338 will be omitted. The basic configuration, action, and effectof the lug groove 327 are similar to those of the lug groove 326, sothat the description of the lug groove 327 will be omitted.

The fourth embodiment is similar to the third embodiment in thepositions and lengths of a central inclined groove 334, a first inclinedgroove 336, and the lug groove 326. However, the fourth embodimentdiffers from the third embodiment in the shape and position of thebottom raising portion formed in each inclined groove.

(First Inclined Groove)

A first bottom raising portion 342 which raises the groove bottom isformed near a first inner major groove-side end 336J of the firstinclined groove 336, so that the first inclined groove 336 issubstantially opened to and terminated in a first inner major groove324A.

A cross section of the first bottom raising portion 342 in the tirewidth direction (longitudinal direction of the groove) is formed in achevron shape, and a first edge line 344 is formed in parallel with thetire circumferential direction at a top portion 342U. A first innermajor groove-side first inclined surface 345 and a first outer majorgroove-side first inclined surface 346 are formed as the groove bottomsurface in the first bottom raising portion 342 (see FIG. 9B). In thefirst inner major groove-side first inclined surface 345, the groovedepth is gradually increased from the first edge line 344 toward thefirst inner major groove 324A. In the first outer major groove-sidefirst inclined surface 346, the groove depth is gradually increased fromthe first edge line 344 toward a first outer major groove-side end 342Kat the first bottom raising portion 342. In the fourth embodiment, thesurface height of the first edge line 344 is equalized to the surfaceheight (namely, height of wheel tread F) of a land portion 331 adjacentto the first inclined groove 336. Accordingly, the depth from the wheeltread F to the first edge line 344 becomes 0 mm.

An edge portion 331E of the land portion 331 on the first inner majorgroove side has an edge surface 331ES that is provided along the firstinner major groove 324A and is chamfered in the tapered shape. The firstinner major groove-side first inclined surface 345 is inclined at aninclination angle θ₁ with respect to the tire radial direction such thatthe first inner major groove-side first inclined surface 345 has thesame plane as the edge surface 331ES. Accordingly, the position of thefirst edge line 344 in the tire width direction is set at the sameposition as an upper edge of the edge surface 331ES. The inclinationangle θ₁ is set in the range of 30 to 60°.

(Central Inclined Groove)

A central bottom raising portion 352 which raises the groove bottom isformed near a first inner major groove-side end 334J of the centralinclined groove 334, so that the central inclined groove 334 issubstantially opened to and terminated in the first inner major groove324A.

As with the first bottom raising portion 342, a cross section of thecentral bottom raising portion 352 in the tire width direction(longitudinal direction of the groove) is formed in a chevron shape, anda central edge line 354 is formed in parallel with the tirecircumferential direction at a top portion of the central bottom raisingportion 352. A first inner major groove-side central inclined surface355 and a second inner major groove-side central inclined surface 356are formed in the central bottom raising portion 352. In the first innermajor groove-side central inclined surface 355, the groove depth isgradually increased from the central edge line 354 toward the firstinner major groove 324A. In the second inner major groove-side centralinclined surface 356, the groove depth is gradually increased from thecentral edge line 354 toward a second inner major groove-side end 352Kof the central bottom raising portion 352. In the fourth embodiment, thesurface height of the central edge line 354 is equalized to the surfaceheight (namely, height of wheel tread F) of a land portion 329 adjacentto the central inclined groove 334. Accordingly, the depth from thewheel tread F to the central edge line 354 becomes 0 mm.

An edge portion 329E of the land portion 329 on the first inner majorgroove side has an edge surface 329ES which is provided along the firstinner major groove 324A and is chamfered in the tapered shape. In thefirst inner major groove-side central inclined surface 355, theinclination angle θ₁ is set with respect to the tire radial directionsuch that the first inner major groove-side central inclined surface 355has the same plane as the edge surface 329ES. Accordingly, the positionof the central edge line 354 in the tire width direction is set at thesame position as an upper edge of the edge surface 329ES. Theinclination angle θ₁ is set in the range of 30 to 60°.

(Lug Groove)

A lug groove bottom raising portion 372 which raises the groove bottomis formed near a first outer major groove-side end 326J of the luggroove 326, so that the lug groove 326 is substantially opened to andterminated in a first outer major groove 322A.

A cross section of the lug groove bottom raising portion 372 in the tirewidth direction (longitudinal direction of the groove) is formed in achevron shape, and a lug groove edge line 374 is formed in parallel withthe tire circumferential direction at a top portion of the lug groovebottom raising portion 372. A first outer major groove-side lug grooveinclined surface 375 and a tread end-side lug groove inclined surface376 are formed in the lug groove bottom raising portion 372. In thefirst outer major groove-side lug groove inclined surface 375, thegroove depth is gradually increased from the lug groove edge line 374toward the first outer major groove 322A. In the tread end-side luggroove inclined surface 376, the groove depth is gradually increasedfrom the lug groove edge line 374 toward a tread end-side end 372K. Inthe fourth embodiment, the surface height of the lug groove edge line374 is equalized to the surface height (namely, height of wheel tread F)of a land portion 331 adjacent to the lug groove 326. Accordingly, thedepth from the wheel tread F to the lug groove edge line 374 becomes 0mm.

An edge portion 325E of the land portion 325 on the first outer majorgroove side has an edge surface 325ES which is provided along the firstouter major groove 322A and is chamfered in the tapered shape. In afirst outer major groove-side lug groove inclined surface 375, theinclination angle θ₁ is set with respect to the tire radial directionsuch that the first outer major groove-side lug groove inclined surface375 has the same plane as the edge surface 325ES. Accordingly, theposition of the lug groove edge line 374 in the tire width direction isset at the same position as an upper edge of the edge surface 325ES. Theinclination angle θ₁ is set in the range of 30 to 60°.

As described above, in the fourth embodiment, the first inner majorgroove-side central inclined surface 355 and the edge surface 329ES formthe same plane, the first inner major groove-side first inclined surface345 and the edge surface 331ES also form the same plane, and the firstouter major groove-side lug groove inclined surface 375 and the edgesurface 325ES also form the same plane. Accordingly, the rigidity isenhanced in each of the edge portions where the edge surfaces areformed, and the roadholding ability is improved on the dry road surface.In the wet road surface driving, the water flows along the respectivetwo surfaces forming the same plane without generating the turbulence,so that the wet drainage property is further improved.

Fifth Embodiment

Then, a fifth embodiment will be described with reference to FIG. 10A.In a pneumatic tire according to the fifth embodiment, when comparedwith the fourth embodiment, a first outer major groove 422A is formed inplace of the first outer major groove 322A, a second outer major groove422B is formed in place of the second outer major groove 322B, a firstinner major groove 424A is formed in place of the first inner majorgroove 324A, and a second inner major groove 424B is formed in place ofthe second inner major groove 324B. A central inclined groove 434 isformed in place of the central inclined groove 334, a first inclinedgroove 436 is formed in place of the first inclined groove 336, and asecond inclined groove 438 is formed in place of the second inclinedgroove 338. A lug groove 426 is formed in place of the lug groove 326 onone surface side of the tire equatorial plane CL, and a lug groove 427is formed in place of the lug groove 327 on the other surface side ofthe tire equatorial plane CL. The basic configuration, function, andeffect of the second inclined groove 438 are similar to those of thefirst inclined groove 436, so that the description of the secondinclined groove 438 will be omitted. The basic configuration, function,and effect of the lug groove 427 are similar to those of the lug groove426, so that the description of the lug groove 427 will be omitted.

The fifth embodiment is similar to the fourth embodiment in thepositions and lengths of the central inclined groove 434, first inclinedgroove 436, and lug groove 426. However, the fifth embodiment differsfrom the fourth embodiment in the shape and position of the bottomraising portion formed in each inclined groove.

(First Inclined Groove)

A first bottom raising portion 442 which raises the groove bottom isformed near a first inner major groove-side end 436J of the firstinclined groove 436, so that the first inclined groove 436 issubstantially opened to and terminated in a first inner major groove424A.

A cross section of the first bottom raising portion 442 is formed in achevron shape in the tire width direction (longitudinal direction of thegroove), and a first edge line 444 is formed in parallel with the tirecircumferential direction at a top portion of the first bottom raisingportion 442. A first inner major groove-side first inclined surface 445and a first outer major groove-side first inclined surface 446 areformed in the first bottom raising portion 442 (see FIG. 10B). In thefirst inner major groove-side first inclined surface 445, the groovedepth is gradually increased from the first edge line 444 toward thefirst inner major groove 422A. In the first outer major groove-sidefirst inclined surface 446, the groove depth is gradually increased fromthe first edge line 444 toward a first outer major groove-side end 442Kof the first bottom raising portion 442. In the fifth embodiment, theposition of the first edge line 444 is located closer to the center sideof the first inner major groove 424A in the tire width direction thanthe position of an upper edge of an edge surface 431ES of a land portion431. The depth D₂ from the wheel tread F to the first edge line 444 isset such that the first inner major groove-side first inclined surface445 and the edge surface 429ES form the same plane.

(Central Inclined Groove)

A central bottom raising portion 452 which raises the groove bottom isformed near a first inner major groove-side end 434J of the centralinclined groove 434, so that the central inclined groove 434 issubstantially opened to and terminated in a first inner major groove422A.

As with the first bottom raising portion 442, a cross section of thecentral bottom raising portion 452 is formed in a chevron shape in thetire width direction (longitudinal direction of the groove), and acentral edge line 454 is formed in parallel with the tirecircumferential direction at a top portion of the first bottom raisingportion 442. A first inner major groove-side central inclined surface455 and a second inner major groove-side central inclined surface 456are formed in the central bottom raising portion 452. In the first innermajor groove-side central inclined surface 455, the groove depth isgradually increased from the central edge line 454 toward the firstinner major groove 422A. In the second inner major groove-side centralinclined surface 456, the groove depth is gradually increased from thecentral edge line 454 toward a second inner major groove-side end 452Kof the central bottom raising portion 452. In the fifth embodiment, theposition of the central edge line 454 in the tire width direction islocated closer to the center side of the first inner major groove 424Athan the position of an upper edge of an edge surface 429ES of aadjacent land portion 429. The depth D₂ from the wheel tread F to thecentral edge line 454 is set such that the first inner major groove-sidecentral inclined surface 455 and the edge surface 429ES form the sameplane.

(Lug Groove)

A lug groove bottom raising portion 472 which raises the groove bottomis formed near a first outer major groove-side end 426J of the luggroove 426, so that the lug groove 426 is substantially opened to andterminated in the first inner major groove 422A.

A cross section of the lug groove bottom raising portion 472 is formedin a chevron shape in the tire width direction (longitudinal directionof the groove), and a lug groove edge line 474 is formed in parallelwith the tire circumferential direction at a top portion of the luggroove bottom raising portion 472. A first outer major groove-side luggroove inclined surface 475 and a tread end-side lug groove inclinedsurface 476 are formed in the lug groove bottom raising portion 472. Inthe first outer major groove-side lug groove inclined surface 475, thegroove depth is gradually increased from the lug groove edge line 474toward the first outer major groove 422A. In the tread end-side luggroove inclined surface 476, the groove depth is gradually increasedfrom the lug groove edge line 474 toward a tread end-side end 472K. Inthe fifth embodiment, the position in the tire width direction of thelug groove edge line 474 is located closer to the center side of thefirst outer major groove 422A than the position of an upper edge of anedge surface 425ES of a land portion 425. The depth D₂ from the wheeltread F to the lug groove edge line 474 is set such that the first outermajor groove-side lug groove inclined surface 475 and the edge surface425ES form the same plane.

According to the fifth embodiment, the volume of the lug groove isincreased to improve the wet drainage property in the wet road surfacedriving.

Sixth Embodiment

A pneumatic tire 810 of a sixth embodiment will be described below.

As shown in FIG. 11A, in a wheel tread portion 819 of a tread portion818, a center major groove 817 having the groove depth D₀ and the groovewidth W₀ is formed on the tire equatorial plane CL. On both sides of thetire equatorial plane CL, outside major grooves 822 are formed along thetire circumferential direction at the position close to a quarter pointQ of a width of a wheel tread portion 819. The outside major grooves 822zone the wheel tread portion 819 into a central region 820 and sideregions 821.

Lug grooves 824 are formed at substantially equal intervals in the tirecircumferential direction, and the tire equatorial plane-side endportion of the lug groove 824 is substantially opened to and terminatedin the outside major groove 822.

The end portion in the tire width direction of each lug groove 824 isextended across the tread end such that the water can be drained to theoutside in the tire width direction.

In the central region 820, plural inclined grooves 832 are arranged onboth sides of the tire equatorial plane CL so as to sandwich the tireequatorial plane CL. The inclined groove 832 is opened to the outsidemajor groove 822, and the inclined groove 832 is extended to the centermajor groove 817 while inclined with respect to the tire circumferentialdirection. The inclined groove 832 has the groove depth D₁, and eachinclined groove 832 is substantially opened to and terminated in thecenter major groove 817.

As a result, a land portion row 842 is formed in the central region 820by the center major groove 817, the outside major groove 822, and theinclined grooves 832 adjacent to each other in the tire circumferentialdirection. The land portion rows 842 includes a pair of land portions840 that are provided in parallel each other with respect to the tireequatorial plane CL.

During the on-load tire rotating operation, when the pneumatic tire 810is rotated to move the ground contact surface toward a U direction, theinclined grooves 832 separated by the tire equatorial plane are inclinedtoward the opposite directions with respect to tire circumferentialdirection such that the groove edge of the inclined groove 832 issequentially in contact with the road surface from the center majorgroove 817 side of the inclined groove 832 toward the outside majorgroove 822 side. Thus, the inclined grooves 832 are formed such that thedirectional pattern is formed, and thereby the drainage property can besecured with the inclined grooves 832 corresponding to a stream line.

A bottom raising portion 839 which raises the groove bottom is formednear the terminal of the inclined groove 832. The bottom raising portion839 whose cross section is formed in the chevron shape includes anoutside inclined surface 836 and an inside inclined surface 838 (seeFIG. 11B). The outside inclined surface 836 forms the outside groovebottom of the inclined groove 832 in the tire width direction. Theinside inclined surface 838 forms the inside groove bottom in the tirewidth direction of the inclined groove 832.

An edge portion 843 of the land portion 840 on the side of the centermajor groove 817 is formed along the center major groove 817 and ischamfered in the tapered shape so as to have an inclined surface 844which forms the same surface as the inside inclined surface 838 (seeFIG. 11C).

A groove length L₁ of a groove portion 832PE in which the outsideinclined surface 836 is formed as the groove bottom (in other words, thegroove length L₁ of the groove portion 832PE in which the groove depthis gradually increased from the later-mentioned edge line 846) rangesfrom 5 to 40% of a tire ground contact width W. A groove length L₂ of agroove portion 832PC in which the inside inclined surface 838 is formedas the groove bottom ranges from 8 to 45% of a width W₀ of the centermajor groove 817.

The edge portion 843 is substantially parallel to the tirecircumferential direction. An edge line 846 formed by the outsideinclined surface 836 and the inside inclined surface 838 issubstantially parallel to the tire circumferential direction. The edgeline 846 forms a top portion of the bottom raising portion 839.

The edge line 846 is formed in parallel with the wheel tread portion819. The surface height of the edge line 846 is set to the same surfaceheight of the land portion 840 (namely, the height of the wheel tread),so that the depth of the edge line 846 from the wheel tread becomes 0mm.

As described above, in the sixth embodiment, the tread wheel pattern isformed in the wheel tread portion 819, and the bottom raising portion839 having the chevron shape in cross section is formed in the inclinedgroove 832. Therefore, in the wet road surface driving, the water nearthe central portion in the tire width direction of the wheel treadportion 819 is distributed into the water flowing into the center majorgroove 817 by the inside inclined surface 838 and the water flowing inthe inclined groove 832 toward the outside in the tire width directionby the outside inclined surface 836. Therefore, the pneumatic tire ofthe sixth embodiment has the excellent wet drainage property.

The roadholding ability on the dry road surface and the unevenwear-resistant property are improved, because the rigidity is enhancedin the corner portion (particularly, the corner portion 841 of theadjacent land portion 840 which has an acute angle when viewed from theside of the wheel tread F) by the bottom raising portion 839.

The edge portion 843 of the land portion 840 on the side of the centermajor groove 817 is provided along the center major groove 817 and ischamfered in the tapered shape so as to have the same surface as theinside inclined surface 838. Accordingly, the rigidity of the edgeportion 843 is enhanced to improve the roadholding ability on the dryroad surface. In the wet road surface driving, the water flows along thesurfaces of the edge portion 843 and inside inclined surface 838 withoutgenerating the turbulence, so that the wet drainage property is furtherimproved.

The edge portion 843 is substantially parallel to the tirecircumferential direction, and the edge line 846 formed by the outsideinclined surface 836 and the inside inclined surface 838 issubstantially parallel to the tire circumferential direction. Therefore,the water near the central portion in the tire width direction of thewheel tread portion 819 is further easily distributed into the waterflowing into the center major groove 817 by the inside inclined surface838 and the water flowing in the inclined groove 832 toward the outsidein the tire width direction by the outside inclined surface 836.Accordingly, the pneumatic tire of the sixth embodiment has theexcellent wet drainage property.

Seventh Embodiment

A seventh embodiment will be described below. As shown in FIG. 12A, thepneumatic tire of the seventh embodiment differs from that of the sixthembodiment in the shape and position of a bottom raising portion 849formed in an inclined groove 852 of a wheel tread portion 850.

The bottom raising portion 849 which raises the groove bottom is formednear the terminal of the inclined groove 852. The bottom raising portion849 whose cross section in the tire width direction is formed in thechevron shape includes an outside inclined surface 856 and an insideinclined surface 858 (see FIG. 12B). The outside inclined surface 856forms the outside groove bottom of the inclined groove 852 in the tirewidth direction. An inside inclined surface 858 forms the inside groovebottom of the inclined groove 852 in the tire width direction.

The position of an edge line 857 formed by the outside inclined surface856 and the inside inclined surface 858 in the tire width direction islocated closer to the position near the tire equatorial plane CL whencompared with the sixth embodiment. The edge line 857 is formed inparallel to the wheel tread portion 850, and the surface height of theedge line 857 is set deeper than the surface height of the land portion840 (namely, height of wheel tread F) by D₂. The inside inclined surface858 and the inclined surface 844 at the edge portion 843 of the landportion 840 form the same surface.

According to the seventh embodiment, in addition to the effect of thesixth embodiment, the groove volume is increased in the region of thebottom raising portion 849 where the inclined groove has the chevronshape in cross section. Therefore, the wet drainage property isexcellent in the wet road surface driving.

Eighth Embodiment

An eighth embodiment will be described below. As shown in FIG. 13A, apneumatic tire of the eighth embodiment differs from that of the sixthembodiment in the shape and position of a bottom raising portion 859formed in an inclined groove 862 of a wheel tread portion 860.

The bottom raising portion 859 which raises the groove bottom is formednear the terminal of the inclined groove 862. The bottom raising portion859 whose cross section in the tire width direction is formed in thechevron shape includes an outside inclined surface 866, a top-portionplane 865, and the inside inclined surface 838 (see FIG. 13B). Theoutside inclined surface 866 forms the outside groove bottom of theinclined groove 862 in the tire width direction. The top-portion plane865 is continued to the tire equatorial plane side of the outsideinclined surface 866, and the height of the top-portion plane 865 issimilar to that of the land portion 840. The inside inclined surface 838described in the sixth embodiment is continued to tire equatorial planeside of the top-portion plane 865.

A width L₃ of the top-portion plane 865 in the tire width direction isnot more than 3 mm.

According to the eighth embodiment, in addition to the effect of thesixth embodiment, the rigidity is enhanced in the corner portion of theland portion 840 adjacent to the bottom raising portion 859. Therefore,the roadholding ability on the dry road surface and the unevenwear-resistant property are improved.

Ninth Embodiment

A pneumatic tire 910 of a ninth embodiment will be described below.

As shown in FIG. 14A, in a wheel tread portion 919 of a tread portion918, circumferential major grooves 922A and 922B are formed along thetire circumferential direction both sides of the tire equatorial planeCL, and the circumferential major grooves 922A and 922B are formed atthe position close to a quarter point Q of a width of a wheel treadportion 919. The circumferential major grooves 922A and 922B zone thewheel tread portion 919 into a central region 920 and side regions 921.

Lug grooves 924 are formed at substantially equal intervals in the tirecircumferential direction, and the tire equatorial plane-side endportion of the lug groove 924 is substantially opened to thecircumferential major grooves 922A or 922B.

The end portion in the tire width direction of each lug groove 924 areextended across the tread end such that the water can be drained to theoutside in the tire width direction.

In the central region 920, on the right of the tire equatorial plane CLon FIG. 14A, plural first inclined grooves 926 are formed atsubstantially equal intervals in the tire circumferential direction. Thefirst inclined groove 926 is completely opened to the circumferentialmajor groove 922A, and the first inclined groove 926 is extended towardthe tire center while inclined with respect to the tire circumferentialdirection. On the left of the tire equatorial plane CL on FIG. 14,plural second inclined grooves 928 are formed at substantially equalintervals in the tire circumferential direction. The second inclinedgroove 928 is completely opened to the circumferential major groove922B, and the second inclined groove 928 is extended toward the tirecenter while inclined with respect to the tire circumferentialdirection. The first inclined groove 926 is substantially opened to andterminated at the groove wall of the second inclined groove 928. Thesecond inclined groove 928 is terminated while not opened to otherinclined grooves.

As a result, a land portion row 929 including land portions 931 isformed in the central region 920. The land portions 931 are formed atsubstantially equal intervals in the tire circumferential direction, andthe land portion 931 is zoned by the circumferential major groove 922,the first inclined groove 926, and the second inclined groove 928.

Thus, in the ninth embodiment, the pairs of inclined grooves includingthe first inclined groove 926 and the second inclined groove 928 arearrayed at substantially equal intervals in the tire circumferentialdirection. During the on-load tire rotating operation, when thepneumatic tire 910 is rotated to move the ground contact surface towardthe U direction, the first inclined groove 926 and the second inclinedgroove 928 are inclined toward the opposite directions with respect totire circumferential direction such that the groove edges of the firstinclined groove 926 and second inclined groove 928 are sequentially incontact with the road surface from the tire center toward the side ofthe circumferential major groove 922. Thus, the first inclined groove926 and the second inclined groove 928 are formed so as to form thedirectional pattern, and thereby the drainage property can be securedwith the inclined grooves corresponding to the flowing direction.

A bottom raising portion 930 which raises the groove bottom of the firstinclined groove 926 is formed in the terminal portion of the firstinclined groove 926. As a result, the first inclined groove 926 issubstantially opened to and terminated at the groove wall of the secondinclined groove 928 (also see FIG. 14B).

A cross section of the bottom raising portion 930 in the tire widthdirection (longitudinal direction of the groove) is formed in a chevronshape, a first terminal 926J has the highest peak where an edge line 934is formed, and a first inclined surface 936 is formed as the groovebottom surface. In the bottom raising portion 930, the groove depth isgradually increased from the first terminal 926J toward acircumferential major groove-side end 930K at the bottom raising portion930 (namely, the groove depth is gradually decreased from thecircumferential major groove-side end 930K toward the first terminal926J at the bottom raising portion 930).

The edge line 934 is formed in a top portion 930U of the bottom raisingportion 930 (see FIG. 14B), and the edge line 934 is located on anopened-side groove edge line 928E of the second inclined groove 928.

A groove length L₁ of a groove portion 926P in which the first inclinedsurface 936 is formed as the groove bottom surface is set in the rangeof 5 to 100% of the groove length of the first inclined groove 926having the groove portion 926P.

D₂ is a groove depth of the first inclined groove 926, and L₀ is alength in which the first inclined groove 926 is opened to the secondinclined groove 928, i.e., the length of the edge line 934. The secondinclined groove 928 has the groove depth of D₁. θ₁ is an inclinationangle at the terminal portion of the first inclined groove 926 withrespect to the tire circumferential direction, and θ₂ is an inclinationangle at the terminal portion of the second inclined groove 928 withrespect to the tire circumferential direction.

In the ninth embodiment, the surface height of the edge line 934 isequalized to the surface height (namely, height of wheel tread F) of theland portion 931. Accordingly, the depth D₃ from the wheel tread F tothe edge line 934 becomes 0 mm in the ninth embodiment.

As described above, in the ninth embodiment, the tread wheel pattern isformed in the wheel tread portion 919, the bottom raising portion 930 isformed while having the chevron shape in cross section, and the edgeline 934 is located on the opened-side groove edge line 928E. Therefore,in the wet road surface driving, the water near the bottom raisingportion 930 of the wheel tread portion 919 is distributed into the waterwhich flows into the circumferential major groove 922A through the firstinclined groove 926 while guided by the first inclined surface 936 andthe water which flows into the circumferential major groove 22B throughthe second inclined groove 928. Accordingly, the pneumatic tire havingthe excellent wet drainage property is obtained in the ninth embodiment.

The rigidity in the tire width direction is increased by the bottomraising portion 930 at a corner portion 931B of the land portion havingthe large angle formed between the first inclined groove 926 and thesecond inclined groove 928. And the rigidity in the tire circumferentialdirection is increased by the bottom raising portion 930 at a cornerportion 931S of the land portion having the small angle. Accordingly,the roadholding ability on the dry road surface and the unevenwear-resistant property are improved.

Tenth Embodiment

A tenth embodiment will be described below. As shown in FIG. 15, apneumatic tire of the tenth embodiment differs from that of the ninthembodiment in a tread pattern formed in a central region of a wheeltread portion 939.

On the right of FIG. 15 of the tire equatorial plane CL of the centralregion, first inclined grooves 946 are formed like the first inclinedgrooves 926 described in the ninth embodiment. In the first inclinedgroove 946, a first bottom raising portion 940 is formed like the bottomraising portion 930 described in the ninth embodiment.

On the left of the tire equatorial plane CL at the central region onFIG. 15, second inclined grooves 948 are formed in place of the secondinclined groove 928 described in the ninth embodiment. The tenthembodiment differs largely from the ninth embodiment in that a secondbottom raising portion 942 whose cross sectional view in the tire widthdirection is similar to that of the first bottom raising portion 940 isformed in the terminal portion of the second inclined groove 948. Thesecond inclined groove 948 is substantially opened to and terminated atthe groove wall of the first inclined groove 946.

As a result, a first edge line 944 formed in a top portion 940U of thefirst bottom raising portion 940 and the second edge line 945 formed inthe top portion of the second bottom raising portion 942 are arranged ina zigzag manner along the tire circumferential direction. In the firstbottom raising portion 940, a first inclined surface 941 is formed likethe first inclined surface 936 in the ninth embodiment. In the secondbottom raising portion 942, a second inclined surface 943 is formed likethe first inclined surface 941. In the second inclined surface 943, thegroove depth is gradually increased from the second edge line 945 to theside of the circumferential major groove 922B.

A zigzag appearance circumferential minor groove 950 which issubstantially continued in the tire circumferential direction is formedin the tenth embodiment. Accordingly, in the wet road surface driving,the water in the region where the zigzag appearance circumferentialminor groove 950 is arranged in the wheel tread portion is distributedinto both sides of the first edge line 944 and the second edge line 945.Therefore, the wet drainage property is further improved.

Experimental Examples

The inventor performs experiments to compare the pneumatic tireaccording to the invention and the conventional pneumatic tire in theperformance. In the experimental example, the sizes of all the pneumatictires are PSR 225/45R17 and the tread width (in loading JATMAmeasurement standard internal pressure) is 180 mm.

The tires are attached to the actually running vehicle, the tireinternal pressure is set at 220 kPa, and performance is evaluated byperforming the experiments on the loading condition that two persons geton board in front seats. The performance evaluation includes (1) theroadholding ability on the dry road surface, (2) the hydroplaningproperty, (3) the roadholding ability on the wet road surface, (4) theuneven wear-resistant property, and (5) the pattern noise property.

First, the inventor performs the experiments with the pneumatic tire ofConventional example.

For the pneumatic tire of Conventional example, as shown in FIG. 18A, ina wheel tread portion 719 of a tread portion 718, outer major grooves722 are formed along the circumferential direction on both sides of atire equatorial plane, and the outer major grooves 722 are formed at theposition of a quarter point Q of the width of the wheel tread portion719. The outer major grooves 722 zone the wheel tread portion 719 into acentral region 720 and side regions 721.

As with the pneumatic tire 210 of the third embodiment, in the sidesregions 721, lug grooves 726 are formed at substantially equal intervalsin the tire circumferential direction, and the tire equatorialplane-side end portion of the lug groove 726 is opened to the outermajor groove 722.

In the central region 720, inner major grooves 724 extended in the tirecircumferential direction are formed on both sides of the tireequatorial plane CL respectively. The inner major groove 724 is arrangedat the position where the distance between the inner major grooves 724is substantially equalized to the distance between the outer majorgroove 722 and the inner major groove 724. The inner major groove 724and the outer major groove 722 have the groove depth D₀.

In the central region 720, inclined grooves 736 are formed atsubstantially equal intervals in tire circumferential direction on bothsides of the tire equatorial plane CL. The inclined groove 736 is openedto the outer major groove 722 and the inner major groove 724, and theinclined groove 736 is extended while inclined with respect to the tirecircumferential direction. The inclination direction of the inclinedgroove 736 is similar to that of the pneumatic tire 210 of the thirdembodiment. As a result, land portion rows 730 including the landportions 731 are formed. A pair is formed by the two land portions 731with respect to the tire equatorial plane CL, and the land portion 731is formed by the outer major groove 722, the inner major groove 724, andthe inclined grooves 736 adjacent to each other in the tirecircumferential direction.

Central inclined grooves 734 are formed at substantially equal intervalsin tire circumferential direction. The central inclined groove 734 isopened to the inner major grooves 724 located on both sides of the tireequatorial plane CL, and the central inclined groove 734 is extendedwhile inclined with respect to the tire circumferential direction. Theinclination direction of the central inclined groove 734 is similar tothat of the pneumatic tire 210 of the third embodiment. As a result, acentral land portion row 728 including the land portion 729 is formed.The land portion 729 crossing the tire equatorial plane CL is formed bythe inner major grooves 724, and the central inclined grooves 734adjacent to each other in the tire circumferential direction.

The inclined groove 736 and the central inclined groove 734 have thegroove length L₀ and the groove depth D₁.

Table 5 shows the tread pattern conditions of the pneumatic tire ofConventional example.

TABLE 5 Pneumatic tire of Pneumatic Pneumatic Pneumatic Conventionaltire of tire of tire of example Example 1 Example 2 Example 3 Groovewidth of 8.3 8.3 8.3 8.3 major groove D0 (mm) Groove width of 6.7 6.76.7 6.7 inclined groove D1 (mm) Groove length 32 32 32 32 of inclinedgroove L0 (mm) Groove length 16 7E 16 of groove portion L1 (mm)Inclination 45 45 angle θ1 (°) Depth of top 0 0 1 portion D2 (mm)

In the experiment in which the conventional pneumatic tire is used, eachindex of the performance evaluation is defined as follows. (1) For theroadholding ability on the dry road surface, the roadholding ability isdefined by feeling during which the vehicle runs in various drivingmodes on the dry circuit course, and the index is set at 100 for areference value. (2) For the hydroplaning property, the vehicle runs onthe wet road surface whose water depth is 10 mm, and the hydroplaninggeneration speed is measured. The index is set at 100 for the referencevalue. (3) For the roadholding ability on the wet road surface, theroadholding ability is defined by feeling during which the vehicle runsin various driving modes on the wet circuit course, and the index is setat 100 for the reference value. (4) For the uneven wear-resistantproperty, a wear step between the blocks adjacent to each other in thetire circumferential direction and a difference in wear amount betweenthe central region 720 and the side regions (shoulder region) 721 aremeasured after 5000 km driving on a general road, and the index is setat 100 for the reference value. (5) For the pattern noise property, anoise amount is measured in the vehicle during when the vehicle runs onthe smooth road surface at a speed of 60 km/h, and the index is set at100 for the reference value.

Table 6 shows the indexes.

TABLE 6 Pneumatic tire of Pneumatic Pneumatic Pneumatic Conventionaltire of tire of tire of example Example 1 Example 2 Example 3Roadholding ability 100 105 110 108 on dry road surface Hydroplaningproperty 100 105 105 106 Roadholding ability 100 105 108 110 on wet roadsurface Uneven wear-resistant 100 105 110 109 property Pattern noiseproperty 100 105 110 108

The inventor uses the pneumatic tire 210 according to the thirdembodiment as the pneumatic tire of Example 1. In the pneumatic tire ofExample 1, the tread pattern is formed under the conditions shown inTable 5.

The experiment is performed under the same conditions as the pneumatictire of Conventional example. (1) For the roadholding ability on the dryroad surface, the index which becomes relative evaluation for thepneumatic tire of Conventional example is computed by the feeling of thedriver. (2) For the hydroplaning property, the hydroplaning generationlimit speed is measured to compute the index which becomes relativeevaluation for the pneumatic tire of Conventional example. (3) For theroadholding ability on the wet road surface, the index which becomesrelative evaluation for the pneumatic tire of Conventional example iscomputed by the feeling of the driver. (4) For the uneven wear-resistantproperty, similarly the wear step and the difference are measured tocompute the index which becomes relative evaluation for the pneumatictire of Conventional example. (5) For the pattern noise property, thenoise amount is measured in the vehicle during when the vehicle runs onthe smooth road surface at the speed of 60 km/h, and the index whichbecomes relative evaluation for the pneumatic tire of Conventionalexample is computed. Table 6 shows the computed indexes.

In Table 6, it is indicated that, as the index is increased, theperformance becomes better. That is, when the index is increased, theroadholding ability on the dry road surface or wet road surface becomesbetter, the hydroplaning generation speed is increased, the wear step orwear amount is decreased, and the pattern noise is decreased.

The inventor also uses the pneumatic tire according to the fourthembodiment as the pneumatic tire of Example 2. In the pneumatic tire ofExample 2, the tread pattern is formed under the conditions shown inTable 5.

In the experiment in which the pneumatic tire of Example 2 is used, aswith the pneumatic tire of Example 1, the indexes which become therelative evaluation are computed for (1) the roadholding ability on thedry road surface, (2) the hydroplaning property, (3) the roadholdingability on the wet road surface, (4) the uneven wear-resistant property,and (5) the pattern noise property. Table 6 shows the computed indexes.

The inventor uses the pneumatic tire according to the fifth embodimentas the pneumatic tire of Example 3. In the pneumatic tire of Example 3,the tread pattern is formed under the conditions shown in Table 5.

In the experiment in which the pneumatic tire of Example 3 is used, aswith the pneumatic tires of Examples 1 and 2, the indexes which becomethe relative evaluation are computed for (1) the roadholding ability onthe dry road surface, (2) the hydroplaning property, (3) the roadholdingability on the wet road surface, (4) the uneven wear-resistant property,and (5) the pattern noise property. Table 6 shows the computed indexes.

As is clear from Table 6, the pneumatic tires of Examples 1 to 3 havethe good capabilities for all the performance evaluations (1) to (5)compared with the pneumatic tire of Conventional example.

Thus, the embodiments of the invention are explained only by way ofexample. However, various changes and modifications could be madewithout departing from the scope of the invention. Obviously the rightrange of the invention is not limited to the above embodiments.

In the invention, the circumferential major groove is not limited to onewhich is linearly extended in the tire circumferential direction. Forexample, a circumferential major groove which is extended in the tirecircumferential direction in a zigzag manner may be used as thecircumferential major groove of the invention. However, in the casewhere the circumferential major groove is formed in the zigzag manner,in order to secure the drainage property, it is preferable to secure aportion through which the water passes linearly in the tirecircumferential direction, that is the so-called see-through portiongroove (a spatial portion which is continued in the circumferentialdirection while not obstructed by a projection (projected in the tirewidth direction) of a side wall in a bent portion of the circumferentialmajor groove formed as the zigzag manner).

INDUSTRIAL APPLICABILITY

As described above, the pneumatic tire according to the invention issuitable to for the attachment to the vehicle in which the high wetperformance is required.

EXPLANATION OF THE REFERENCE NUMERALS

-   10 pneumatic tire-   12 tread-   12A wheel tread-   14 circumferential wide major groove-   16 first narrow circumferential minor groove-   18 second narrow circumferential minor groove-   20 first transverse grooves-   22 second transverse groove-   24 third transverse groove-   26 first block-   28 second block-   30 stepping-on-side third block-   32 kickout-side third block-   CL tire equatorial plane-   110 pneumatic tire-   112 tread-   112A wheel tread-   114 circumferential wide major groove-   116 first narrow circumferential minor grooves-   118 second narrow circumferential minor grooves-   120 first transverse grooves-   122 second transverse grooves-   126 first block-   128 second block-   130 stepping-on-side third block-   132 kickout-side third block-   210 pneumatic tire-   219 wheel tread portion-   222A first outer major groove (circumferential major groove)-   222B second outer major groove (circumferential major groove)-   224A first inner major groove (circumferential major groove)-   224B second inner major groove (circumferential major groove)-   226 lug grooves (transverse groove)-   226J first outer major groove-side end (one end in tire width    direction)-   226P groove portion-   228 central land portion row (land portion row)-   229 land portion-   230 first adjacent land portion row (land portion row)-   231 land portion-   232 second adjacent land portion row (land portion row)-   233 land portion-   234 central inclined grooves (transverse groove)-   234J first inner major groove-side end (one end in tire width    direction)-   234K second inner major groove-side end (other end in the tire width    direction)-   234P groove portion-   236 first inclined groove (transverse groove)-   236J first inner major groove-side end (one end in tire width    direction)-   236K first outer major groove-side end (other end in the tire width    direction)-   236P groove portion-   238 second inclined groove (transverse groove)-   238J second inner major groove-side end (one end in tire width    direction)-   238K second outer major groove-side end (other end in the tire width    direction)-   238P groove portion-   242 first bottom raising portion (bottom raising portion)-   246 first inclined surface (inclined surface)-   252 central bottom raising portion (bottom raising portion)-   256 central inclined surface (inclined surface)-   262 second bottom raising portion (bottom raising portion)-   266 second inclined surface (inclined surface)-   272 lug groove bottom raising portion-   322A first outer major groove (circumferential major groove)-   322B second outer major groove (circumferential major groove)-   324A first inner major groove (circumferential major groove)-   324B second inner major groove (circumferential major groove)-   325 land portion-   325E edge portion-   325ES edge surface-   326 lug grooves (transverse groove)-   326J first outer major groove-side end (one end in tire width    direction)-   327 lug groove-   329 land portion-   329E edge portion-   329ES edge surface-   331 land portion-   331E edge portion-   331ES edge surface-   334 central inclined grooves (transverse groove)-   334J first inner major groove-side end (one end in tire width    direction)-   336 first inclined groove (transverse groove)-   336J first inner major groove-side end (one end in tire width    direction)-   342 first bottom raising portion (bottom raising portion)-   342U top portion-   345 first inner major groove-side first inclined surface    (one-end-side inclined surface)-   346 first outer major groove-side first inclined surface (inclined    surface)-   352 central bottom raising portion (bottom raising portion)-   355 first inner major groove-side central inclined surface    (one-end-side inclined surface)-   356 second inner major groove-side central inclined surface    (inclined surface)-   372 lug groove bottom raising portion-   375 first outer major groove-side lug groove inclined surface-   376 tread end-side lug groove inclined surface (inclined surface)-   422A first outer major groove (circumferential major groove)-   422B second outer major groove (circumferential major groove)-   424A first inner major groove (circumferential major groove)-   424B second inner major groove (circumferential major groove)-   434 central inclined grooves (transverse groove)-   436 first inclined groove (transverse groove)-   438 second inclined groove (transverse groove)-   426 lug grooves (transverse groove)-   427 lug groove-   436J first inner major groove-side end (one end in tire width    direction)-   442 first bottom raising portion (bottom raising portion)-   445 first inner major groove-side first inclined surface (one end in    tire width direction)-   446 first outer major groove-side first inclined surface (inclined    surface)-   434J first inner major groove-side end (one end in tire width    direction)-   452 central bottom raising portion (bottom raising portion)-   455 first inner major groove-side central inclined surface (one end    in tire width direction)-   456 second inner major groove-side central inclined surface    (inclined surface)-   426J first outer major groove-side end (one end in tire width    direction)-   472 lug groove bottom raising portion-   475 first outer major groove-side lug groove inclined surface (one    end in tire width direction)-   476 tread end-side lug groove inclined surface (inclined surface)-   T tread end-   θ1 inclination angle-   810 pneumatic tire-   817 center major groove (groove)-   819 wheel tread portion-   832 inclined grooves-   832PE groove portion-   832PC groove portion-   836 outside inclined surface-   838 inside inclined surface-   839 bottom raising portion-   840 land portion-   843 edge portion-   846 edge line-   849 bottom raising portion-   850 wheel tread portion-   852 inclined groove-   856 outside inclined surface-   857 edge line-   858 inside inclined surface-   859 bottom raising portion-   860 wheel tread portion-   862 inclined groove-   865 top-portion plane-   866 outside inclined surface-   869 wheel tread portion-   877 center major groove (groove)-   882 inclined groove-   890 land portion-   F wheel tread-   910 pneumatic tire-   919 wheel tread portion-   922A, B circumferential major grooves-   926 first inclined grooves (inclined groove)-   926P groove portion-   928 second inclined groove (inclined groove)-   928E opened-side groove edge line-   930 bottom raising portion-   934 edge line-   936 first inclined surface (inclined surface)-   939 wheel tread portion-   940 first bottom raising portion (bottom raising portion)-   941 first inclined surface (inclined surface)-   942 second bottom raising portion (bottom raising portion)-   943 second inclined surface (inclined surface)-   944 first edge line (edge line)-   945 second edge line (edge line)-   946 first inclined groove-   948 second inclined grooves-   950 zigzag appearance circumferential minor groove-   956 first inclined groove (inclined groove)-   958 second inclined groove (inclined groove)-   969 wheel tread portion-   972A, B circumferential major groove-   976 first inclined groove (inclined groove)-   978 second inclined groove (inclined groove)

1. A pneumatic tire comprising at least one circumferential wide majorgroove, a plurality of transverse grooves, and a narrow circumferentialminor groove, wherein, the circumferential wide major groove beingprovided in a center region in a tire width direction of a tread, thecircumferential wide major groove being extended in a tirecircumferential direction, each of the transverse grooves being extendedfrom a tread end toward the circumferential wide major groove whileinclined with respect to the tire circumferential direction, the narrowcircumferential minor groove being arranged on an outside of thecircumferential wide major groove in a tire axis direction, the narrowcircumferential minor groove being extended in the tire circumferentialdirection, a groove width of the narrow circumferential minor groove isset narrower than that of the circumferential wide major groove, thetread having a plurality of blocks which are zoned by thecircumferential wide major groove, at least one of the transversegrooves, and the narrow circumferential minor groove, the tread having adirectional tread pattern in which the each transverse groove beingsequentially in contact with a road surface from a tire equatorial planeside toward the tread end of the transverse grooves during an on-loadrotating operation, a width and a depth of the narrow circumferentialminor groove in an area where the narrow circumferential minor groovezones the block are decreased from a kickout side toward a stepping-onside with respect to the block during the on-load rotating operation,the narrow circumferential minor groove includes a first end connectedto one of the plurality of transverse grooves and a second end connectedto another of the plurality of transverse grooves and two side groovewalls that each extend between the ends, the depth of the narrowcircumferential minor groove is increased toward the kickout side from aportion of the narrow circumferential minor groove where the side groovewalls of the narrow circumferential minor groove are in contact with oneanother, and the narrow circumferential minor groove includes a flatbottom which is parallel to the tread and is disposed at a portion ofthe narrow circumferential groove where the side groove walls of thenarrow circumferential groove are not in contact with one another. 2.The pneumatic tire of claim 1, wherein, at least two narrowcircumferential minor grooves are provided on the outside of thecircumferential wide major groove in the tire axis direction, and theplurality of transverse grooves includes a first transverse groove, asecond transverse groove, and a third transverse groove, the firsttransverse groove being extended from the tread end, the firsttransverse groove being coupled to the circumferential wide major groovewhile intersecting with the narrow circumferential minor grooves, thesecond transverse groove being arranged between the first transversegrooves, the second transverse groove being extended from the tread endand intersecting with the narrow circumferential minor grooves, thesecond transverse groove being terminated while not coupled to thecircumferential wide major groove, the third transverse groove beingarranged between the first transverse groove and the second transversegroove, the third transverse groove being extended from the tread endand terminated between the two narrow circumferential minor grooves. 3.The pneumatic tire of claim 2, wherein tire equatorial plane-sideterminal positions of the second transverse groove and third transversegroove are located in a central region of a block in the tire axisdirection.
 4. The pneumatic tire of claim 2, wherein, assuming that W2is a groove width of the first transverse groove, W3 is a groove widthof the second transverse groove, and W4 is a groove width of the thirdtransverse groove, W3 is set in a range of 60% to 110% of W2 and W4 isset in a range of 20% to 60% of W2.
 5. The pneumatic tire of claim 2,wherein the narrow circumferential minor groove arranged on theoutermost side in the tire axis direction is inclined toward a directionso that the narrow circumferential minor groove is sequentially incontact with the road surface from the tire equatorial plane side towardthe tread end side of the narrow circumferential minor groove during theon-load rotating operation.
 6. The pneumatic tire of claim 1, wherein:the at least two narrow circumferential minor grooves are provided onthe outside of the circumferential wide major groove in the tire axisdirection, the plurality of transverse grooves includes a firsttransverse groove and a second transverse groove, the first transversegroove being extended from the tread end, the first transverse groovebeing coupled to the circumferential wide major groove whileintersecting with the narrow circumferential minor grooves, the secondtransverse groove being arranged between the first transverse grooves,the second transverse groove being extended from the tread end, thesecond transverse groove intersecting with the narrow circumferentialminor groove on an outermost side in the tire axis direction while notintersecting with the narrow circumferential minor groove on aninnermost side in the tire axis direction, the second transverse groovebeing terminated while not coupled to the circumferential wide majorgroove, the first transverse groove has a bottom raising portion at theside of the circumferential wide major groove, and a groove depth of thebottom raising portion is gradually decreased from a start pointprovided at an outside with respect to the circumferential wide majorgroove toward the circumferential wide major groove in the tire axisdirection.
 7. The pneumatic tire of claim 6, wherein, a length of thebottom raising portion in the tire axis direction is set in the range of60 to 200% of a groove width of the circumferential wide major groove.8. The pneumatic tire of claim 6, wherein a depth of a top portion ofthe bottom raising portion is set to 10% or less of a depth of the firsttransverse groove when each depth is measured from a wheel tread surfaceof the tread.
 9. The pneumatic tire of claim 6, wherein the width of thesecond transverse groove is set in the range of 10 to 80% of the widthof the first transverse groove.
 10. The pneumatic tire of claim 1,wherein, in the narrow circumferential minor groove, a groove wall onthe tire equatorial plane side is linearly extended in the tirecircumferential direction and an angle of the groove wall with respectto a normal reference to a wheel tread surface ranges from 40 degrees to80 degrees.
 11. The pneumatic tire of claim 1, wherein, in the narrowcircumferential minor groove, the groove wall on the tire equatorialplane side is coupled to the opposing groove wall on the outside in thetire axis direction at the stepping-on side with respect to the block.